Toyota RAV4 Forums banner

1 - 13 of 13 Posts

·
Registered
Joined
·
17 Posts
Discussion Starter #1
Hello fellow Ravsters

Does anyone know if there is such a thing as a cordless / battery powered trickle-charger for a 12v wet cell car battery?

I’ve scoured the internet for hours and cannot find anything, so I’m guessing not, and that there must be a scientific / physics reason for this I guess.

The problem I have is my wife only drives her RAV4 about once or twice a week these days, and then for only a few miles at low speed / low revs in local traffic. It only gets a longer run (1hr+ at sustained speed / higher revs) about once a month. So usual story. Once winter comes around, even with a new or newish battery, after a couple weeks or so of freezing temps the battery is not dead flat, but low enough not to start (11.70v or less).

I have one of those Li-Ion boost start packs which are excellent, gets it fired up under 3 mins. And then take the car for a 60-90 min run on dual-carriageway / motorway to get battery back to 12.68v

Have to do this 3 or 4 times over winter, then once into spring / summer / autumn generally don’t have the problem. Though do go through a new battery every 2-3 years vs 5-6. But alternator is kicking out good / normal charge. Battery is holding charge (plus it’s only 12 months old). Had both verified by AA service tech. I don’t think there is an excessive parasitic key-off drain (though I’m now monitoring). Only started having this issue 2-3 years ago when the wife started using the car much less. Prior to that never had any battery issues for years. So I’m associating low usage with small battery capacity (it’s just the stock spec 330 CCA / 45aH type, where-as my own car has equally low usage but a 750 CCA / 74aH battery and I don’t have the same problem).

I could just keep up this routine, even though a tad tedious. However, I’ve read multiple times that it really isn’t good for the battery or the alternator (which I’m more concerned about) to be using the car to get back from a sub 12v (<25%) charge to a 12.68v / 100% charge regularly.

Problem is, the car is kept in an underground garage, where there are no (practical) options to use a mains powered trickle-charger. And no sunlight (or even bright enough artificial light) to use a solar powered trickle charger.

Not only is removing the battery on the RAV4 (well this model, circa 2003) a right pain in the a** as fellow owners will know, as requires removing windscreen cowling. But also the car REALLY doesn’t like having the battery removed and gets amnesia on engine management system / ECU et al (aside from the tolerable stuff like losing all radio and sat-nav data). It takes a good couple of days to re-learn it’s optimum idling / fuel use etc, meanwhile constantly stalling (it’s an auto-box!) and really pi**ing off the Mrs, for which I get ear-ache. So removing the battery to trickle charge inside home (or even a second one and hot-swapping) is not really an option I want to pursue on a monthly basis, let alone more frequently.

Other than just running the car on pointless 30-40 mile loop for an hour every week, I was hoping I could find (or maybe even build?) a trickle-charger based on batteries (pref light-weight Li-Ion) which I could charge-up in the home, then place in the footwell and run a lead through closed window into bonnet and leave to maint trickle-charge the 12v car battery overnight once a week to keep it 100%.

Anyone have any ideas / suggestions / know if such a device is possible without having to hook up directly to a mains supply?

Many thanks

TT
 

·
Registered
Joined
·
17 Posts
Discussion Starter #3
Thanks DL175

Yes, I guess a large enough / powerful enough solar panel might well work outdoors (even in cloudy weather), though I have read mixed reports on even the best given the UKs great weather! - esp over winter when this is an issue.

However, parking the car outdoors is not really an option or desirable. It stays in an underground parking garage with minimal natural light and low output sodium lights, so I think even the largest panel would not even keep pace with the normal level of key-off drain let alone top up to 100%.

Hence my search for a battery powered trickle-charger.
 

·
Registered
Joined
·
3,761 Posts
I don't know but maybe a battery pack which has an AC outlet can work? A trickle charger can use 1.5 amp but I don't know how long it can charge for.
 

·
Super Moderator
Joined
·
10,224 Posts
I like DL175's battery booster idea but on a larger scale since what you need is AH and the boosters usually have gel batteries of 10-15AH. I also agree driving the car around just to charge its battery is a big waste - of time, gas and money.
And unless you have some source of energy (which you don't) physics says there is no magic solution. Whatever you do you have to carry the energy to the car.
So here's my solution:
1. Buy a fairly decent sized 12V battery, an RV deep cycle being best. A Lithium motorcycle battery would be a lighter alternative but they are about 3 time the cost.
2. Connect a small efficient DC-to-AC (100-150W?) inverter to it.
3. Connect a small battery charger with say a 2 amp trickle mode to the inverter.
4. Build all this into a box wired to make it easy to switch it into recharge-on-mains mode at a higher charge level, or better yet add a second charger for the recharge.
4. Rig your connection to the car's battery and run it every few days or maybe even continuous depending on how long the battery-in-a-box lasts.
5. Carry it back and forth as often as needed to do the job.
 
  • Like
Reactions: TonkaToy

·
Registered
Joined
·
8,595 Posts
I'm a reluctant risk taker and having lived in the U.K and worked with the 240v system I managed to contrive some interesting and sometimes risky solutions. Since your RAV is in an underground garage, is there a lighting system with a fixture near your parking spot? If so and if it is allowable could it be possible to tap into the supply mains in the light fixture mounting box, run s short lead to a socket box, and plug a lead into the socket which would power a trickle charger? You would need to be very careful as you might have to tap into the mains while they are energized if the power cannot be switched off, which means using insulated tools and gloves. Or hire a licensed electrician to do that or something similar.
 
  • Like
Reactions: TonkaToy

·
Registered
Joined
·
17 Posts
Discussion Starter #7
Thanks again DL and Dr Dyno.

I think there is the beginnings of a heath robinson battery-trickle-charger lash up here. I like the idea of the Lithium motorcycle batteries connected to an inverter and then powering a regular top brand maint charger (CTEK / Optimate etc).

I'm going to start putting a spec together and checking all the power output and requirement of each component in the chain to see if the thing will a)work b) not blow up c) trickle charge for more than 10 mins!

Thanks for the tips. Now to the homework!
 

·
Registered
Joined
·
17 Posts
Discussion Starter #8
Blogson

LOL. Oh believe me, I prowled around the basement garage looking at all the lighting power conduits, the A/C split packs et al, to see if there was any existing spare outlet or something that could be safely DIY spurred. Nope.

It's a leasehold condo. If I did anything unauthorised - even if totally safe and certified, I'd be shot by the managing agent and freeholder. And I know for a fact I would never get permission for an authorised spur. They're miserable b*****s. Hence I'm in this battery lash-up territory. But appreciate the thought!

TT
 

·
Super Moderator
Joined
·
10,224 Posts
Another configuration: Wire the inverter & trickle charger into and leave them attached to the RAV4. Use a quick-connect or even clip leads to connect to the battery. Leave the larger battery charger in the condo. Then you not only only have to transport the battery, but you could start with one lightweight battery and add another one or two in a parallel pack until you get the needed performance.
 

·
Your Humble Administrator
2008 RAV4 Limited V6
Joined
·
16,761 Posts
I don't like the idea of using a battery to send DC to an inverter which converts the DC to AC to power a trickle charger that converts the AC back to DC. This is terribly inefficient. How about rigging up a second battery? It could be a small motorcycle battery that would be sufficient to keep the radio presets and ECM happy while the main battery is idle. A switch to go from aux battery to main battery could be used before starting the engine. I know many RV's have 2 batteries for this reason with a circuit that charges both batteries when the engine is running.
 

·
Super Moderator
Joined
·
10,224 Posts
I don't like the idea of using a battery to send DC to an inverter which converts the DC to AC to power a trickle charger that converts the AC back to DC. This is terribly inefficient.
Yes it's inefficient but it essentially is a booster to raise the voltage from 12 to 13.5-14 to keep the car's battery fully charged at the expense of the second battery. I actually used the technique once on my '99 Diesel to help it start in very cold weather. Took a spare battery, hooked an inverter up to it, plugged the charger into the inverter and hooked the charger output up to the two batteries in the truck. Let it run overnight in bitter cold. Next morning the booster battery was pretty low but the truck cranked over like it was driving 40mph down the road.
How about rigging up a second battery? It could be a small motorcycle battery that would be sufficient to keep the radio presets and ECM happy while the main battery is idle. A switch to go from aux battery to main battery could be used before starting the engine.
If a small battery could keep the system alive why couldn't the car's bigger battery?

I know many RV's have 2 batteries for this reason with a circuit that charges both batteries when the engine is running.
Yep, it's called an isolater but its purpose is essentially the opposite of what we need here - to keep the 12V power and battery in the RV from pulling down the engine's battery below being able to start. Camper lights going dim overnight beats not being able to start the next morning. When we towed my BIL's camper with the RAV4 in Alaska we made sure to disconnect the 7-round trailer cord from the RAV overnight to preclude the same problem.
 

·
Registered
Joined
·
1 Posts
I like DL175's battery booster idea but on a larger scale since what you need is AH and the boosters usually have gel batteries of 10-15AH. I also agree driving the car around just to charge its battery is a big waste - of time, gas and money.
And unless you have some source of energy (which you don't) physics says there is no magic solution. Whatever you do you have to carry the energy to the car.
So here's my solution:
1. Buy a fairly decent sized 12V battery, an RV deep cycle being best. A Lithium motorcycle battery would be a lighter alternative but they are about 3 time the cost.
2. Connect a small efficient DC-to-AC (100-150W?) inverter to it.
3. Connect a small battery charger with say a 2 amp trickle mode to the inverter.
4. Build all this into a box wired to make it easy to switch it into recharge-on-mains mode at a higher charge level, or better yet add a second charger for the recharge.
4. Rig your connection to the car's battery and run it every few days or maybe even continuous depending on how long the battery-in-a-box lasts.
5. Carry it back and forth as often as needed to do the job.

SO -- 9 years later, hoping to get a response...

I have a 2016 RAV4 Hybrid XLE which came with a brand new (2019) hybrid battery and I am looking for a way to keep the hybrid battery charged without driving the car. This idea stood out to me because I could easily build such a box for my car and mount it where the spare tire is, and build an external mount for my spare tire instead. My questions for you are two fold. One hypothetical being that I only use the box when not driving. One being that the box is always feeding the battery and I replace the dead 12v batteries as needed from the box.

In scenario 1, what Amperage and Voltage would I need the inverter and chargers to be and would it work with a simple activation switch I could mount under the dash and wire to the trunk?

In scenario 2, is this even possible without screwing up the electronics? I feel like in this scenario, I would almost be better off making an array of 18650's and plugging it into a wall every week or so.

What are your thoughts?

-Nate
 

·
Super Moderator
Joined
·
10,224 Posts
"9 years later," ????

"an array of 18650's"
What are they?
 
1 - 13 of 13 Posts
Top