[Clemtoo]

Hello,
I had the same problem with extended storage and have no means to connect a battery charger at my parking spot. I purchased another battery to connect the with the main battery (Banner), in parallel. The battery I purchased (Exide) is the same type and capacity as the main battery ( AGM, 80 Ah). In the last 2 years, I did not run the car during a 11 week period, while away on holidays, and when I returned the engine started without a problem, both times, after disconnecting the Excide battery. The last step before leaving on holidays, was to switch off the interior surveillance inclination sensor by pressing the key fob locking button twice within 2 seconds, in order to draw the minimum amount of power. I also have a battery charger in my apartment to fully charge both batteries, but one at a time. The only difficulty is lugging the batteries from my apartment to the parking spot. I think this is better than resetting all the electronics. I do not run the engine when both batteries are connected in parallel. When connecting and disconnecting the batteries you always have to make sure that at least one battery is always connected. You have to carefully think through the steps when connecting and disconnecting the battery cables. I also attached a file telling what to do when battery power is lost.
Cheers

 

[Clemtoo]

That’s A pretty good solution but I was this thread on another board.

It seems they’ve come up with something along the same lines that you’ve come up with.

Create a wiring harness that fits under the hood and is easily accessible and if your battery should go dead simply plug in a “ micro jumper battery “ and hopefully you’ll be on the road pretty painlessly.

Posts #33 and # 38 are where most of the info is.

https://********.com/forums/987-981-forum/1110823-dead-battery-help-up-creek-3.html

I used a Solar Battery and System Tester, Model No. BA9, to show the relative condition of the battery. The test numbers for the Exide battery connected in to the main Banner battery are:
before connecting in parallel to main Banner battery, Exide measurements, V = 13.20, CCA = 744, SOH% = 93, SOC% = 100, mOhms =3.45.
11 weeks later and Exide battery disconnected, Exide measurements, V =12.76, CCA = 638, SOH = 79, SOC% = 96, mOhms = 4.03
2 days later, after Exide disconnected from charger, Exide measurements, V =13.39, CCA = 800, SOH% = 100, SOC% = 100, mOhs - 3.03

Many numbers, but they show the condition of the Exide battery did not deteriorate after 11 weeks being connected in parallel. Didn't take measurements of the main Banner battery after 11 weeks. After disconnecting the Exide battery, after 11 weeks the engine started, no problem with the only main Banner battery connected.