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Has anybody here designed a Factory looking Auxiliary Battery Trickle Charger ?

2.1K views 20 replies 13 participants last post by  The Gadgeteer  
#1 ·
Hi,
I really like the RAV4 Hybrid but it does have it's caveats. It's delivered excellent performance and MPG for family Summer road trips and hauling my r/c airplane, jets, and helicopter gear ro my club's airfield. There's only one shortcoming. The poor design of the Auxiliary Battery. The vehicle has too many overhead head tasks that run while it's shutoff and parked. I am an engineer and I work from home most of the time. If my RAV4 sits parked under the carport for two weeks the aux battery will just about fully discharge. If it's cold, -5F like it is right now the battery will discharge in a week. Yesterday my area got hit with a snowstorm. I went to move my RAV4 from the carport to the driveway and the aux battery was dead. I had to walk through the snow to my shed, get the 12v charger, set it up, charge for 10 minutes, Put the RAV4 in Ready mode and let it sit for 2hrs, and put my 12v charger back in the shed. There should be a gauge on the RAV4 dash with the status of the 12v battery, but it was left out. I purchased a bluetooth 12v battery monitor, the specs rate the current draw at 1.5 mah. When it warms up I will install it. I plan on pulling the DCM fuse as well. The DCM is far too chatty. Telematics should not occur when the vehicle is parked and shutdown. The last status when the vehicle was put in Park should be enough. It's almost as if the lead programmer on the Toyota DCM had OCD. I'm looking for a trickle charge solution that installs under the hood and the harness plug that connects to the trickle charger terminates in the grill in one of the screen/mesh holes on the lower bottom driver's side. That way I can plug it into the AC Outlet that lines up with the front driver's side grill

Ford has a solution for their Hybrid Pickup Trucks. A coworker told me the Ford App is free and he can program it to automatically put the vehicle in Ready mode on a schedule and set the duration for as long as he wants. If the vehicle is in use the connection is ignored.

Toyota can actually learn a lesson from Ford here. The Aux Battery is a PITA during the winter.
 
#2 ·
Under hood on my F-250s and my previous Accord hybrid I use marine battery charger/maintainers made by Guest. They are available in many Ampere ratings and sizes but all are completely waterproof. I probably have half a dozen of them and never had a problem with any even tho most of them are bought used. This one may be the size you need:
Guest ChargePro 5 12V 5Amp On-Board Marine Battery Charger NEW | eBay

BTW, I've bought (won) hundreds of items on eBay by only bidding in the last few seconds. That way others don't have time to outbid you and you can bid high because you only pay enough to win.
 
#3 ·
Another option is to hook up permanent extension leads to aux. battery and extend them to a convenient location on car. This is convenient if you have several batteries and one charger. Discharged batteries often require 12 hours or more to charge depending on battery size, discharge state and charger size. Charging for a couple of hours and then leaving it in a low state of charge is an invitation for another dead battery. Sounds like your battery is toast! If properly charged it should last for at least 3 or 4 weeks unless there are parasitic loads other than normal vehicle devices.
 
#4 ·
. I'm looking for a trickle charge solution that installs under the hood and the harness plug that connects to the trickle charger terminates in the grill in one of the screen/mesh holes on the lower bottom driver's side. That way I can plug it into the AC Outlet that lines up with the front driver's side grill
1. A trickle charger will overcharge a battery and ruin it. You must get a battery maintainer, such as a Battery Tender (name brand) which will not overcharge your battery.
2. What year is your RAV4? The early 5th generation RAV4s used the DCM too much when the car is off, which would discharge the 12 volt battery prematurely. There is a firmware update for the DCM to solve that problem. It is free if you are still under warranty.
3. In Canada, part of the Comfort + (plus) system includes a battery charger: Comfort+ Heating Accessories - Toyota Canada That's as OEM as it gets.
 
#17 ·
1. A trickle charger will overcharge a battery and ruin it. You must get a battery maintainer, such as a Battery Tender (name brand) which will not overcharge your battery.
3. In Canada, part of the Comfort + (plus) system includes a battery charger: Comfort+ Heating Accessories - Toyota Canada That's as OEM as it gets.
This might be a bit of a LOL, but on the page for Comfort+, one of the components of this is a (ahem) TRICKLE CHARGER. I put that in all caps because it's in all caps as a main header item on that page.

One can only assume that Toyota has realized something. Although technically speaking, a "trickle charger" was originally a dumb device, it put out the specified amps, and that's all it did. But modern trickle chargers are actually battery maintainers, AKA "battery tenders" such as the Battery Tender (brand name). Even when searching on Amazon for "trickle charger", the units under $10 are intelligent battery maintainers. I'm not sure you could find a (brand new) trickle charger that is not a battery maintainer.

Back to that search on Amazon - if you sort the "trickle charger" results by Avg Cust Review, the top 2 items are Battery Tender brand. Talk about "stealing the show".

P.S. - No I would not trust a battery maintainer for $10 on Amazon.
 
#5 ·
Comfort + looks exactly like what I was looking for. My RAV4 us a 2022 Hybrid Limited. I'm going to search for alternative install solutions. I was thinking about making a mount for the Plug in socket in the lower driver's side corner of the front grill mesh.

Does the 2022 model have the chatty DCM firmware bug ?
 
#7 ·
Comfort + looks exactly like what I was looking for. My RAV4 us a 2022 Hybrid Limited. I'm going to search for alternative install solutions. I was thinking about making a mount for the Plug in socket in the lower driver's side corner of the front grill mesh.

Does the 2022 model have the chatty DCM firmware bug ?
The Service Bulletin, T-SB-0089-21 is applicable to the 2020 through 2022 RAV4, so yes, your RAV may have the problem. You can print out the T-SB and show it to your dealer.

The Comfort + system is sold only by Toyota dealers in Canada, but you can buy them from a Canadian dealer and install it yourself if you are handy. I don't know if it will fit the Prime, however.
 
#14 ·
An ICE vehicle usually gives a bit of warning when 12v battery is getting tired. Over time engine begins to turn over slower when cold. Natures battery load tester! Usually a big run on batteries around here during the first cold snap when extra cold cranking amps are needed. Hybrid 12v batteries work fine until they don't! No warning. While completely charging battery may help if cause was an accessory left on or vehicle was left unattended for an extended period of time they should be load tested and replaced if degraded.
 
#16 ·
I own a few Battery Tender brand units. I have installed their extension cord directly to the 12 volt battery in back. I cut a small opening and I have the cord (+/- 3 ft) laying on the deck behind the rear seat. So, if I loose power and can't open the rear door, I just open the rear passenger door to hook the Tender up.
I also put all of my cars/trucks on the charger on a regular basis.

Absolutely no problems for my 2022 Limited.