I'm planning on installing a second battery to support winching, extra power for a fridge, lights, and general backup power incase I need to escape my college dorm when the fire alarm goes off for the 3rd time in a week. Anyways I saw a forum thread with the title "LR3: My dual battery / auxiliary battery install" and was planning on doing the same but wanted some general advice when doing this, I'm a bit worried that the additional battery may affect the stock electronics on board (to my understanding to the cars electrical system it will appear like 1 battery, but just want to make sure this is the case), is there any cause for this concern and or side effects for the car? I was also considering putting off-road lights, part time fridge, and a 65watt usb C port for laptops and fast charging phones. Any advice with these mods or things to look out for?

 

If it were me doing it I'd keep the second battery off the vehicle's circuit and use it for all the auxillary equipment. Then I'd use a battery to battery charger to keep it topped off. But this is just my thoughts coming from the van building arena.

 

I was thinking of that, but DC to DC chargers are expensive and I want to be able to use both of them to winch together, and jump start each other if need be. I do like the way they help with battery life but just can't justify it with the budget build

 

In my opinion, there isn't a cheap way to do what you want to do, or at least do it safely.

Connecting them together in parallel will increase your available amps and keep the volts the same, but doing it safely generally means you're using the same battery for both so that they run in as close to the same voltage as possible. Although we refer to them as 12v batteries, they can vary in volts quite a bit. If your two batteries have different natural volts one will always be trying to charge the other, which can lead to heat/swelling issues depending on your battery chemistry.

So I'd guess at the least you'd be looking at two new batteries. As far as charging both, it would depend on their chemistry.

If it were me, I'd be saving and using a LiPo for my house battery, since you can discharge them much further than a standard or AGM battery, and keep the car battery separate. Thay way if you have a parasitic draw on one, you're not killing the other. If you have them connected, and let's say you leave you lights on while out hiking, you've just killed both. If they're separate, you've only killed the car battery, and can use the "house" battery for jump-starting.

 

Duel battery setups are very common in the LR3/D3. People install em all the time. There is no need at all for a DC to DC. It is just a battery, so no it won't harm or cause any issues with the existing electronics. A smart-solenoid can do all the connecting automatically so you dont have to worry about parasitic draws or letting your fridge run things down and take the starting battery along with the drain. You will want to run your winch from the starting battery, it should never be run from the auxiliary. LiPo batteries are nice, but they can be a bit expensive and most will not do well in the engine bay and LiPo batteries can not be charged below freezing. You want a battery that is as close in size to the starting battery as possible and one that is similar in age in order to have a nicely balances system, but if you have a smart solenoid then it is not an issue really.

 

There ya go rikkd ^. Much simpler than when you're playing with multiple charging sources (shore power, solar, b2b), 3000w inverters, etc. Generally in the van builds you want your starter and aux (house) to be separated and have multiple fail-safes, as miswired shore power or rogue inverter can wipe out electronics right quick.

Yeah, LiFePos are expensive and don't charge below freezing, but many now have heater blankets that require just a few amps to get them to charge temp. And they can discharge below freezing, so unless they're 100% empty they can use their own power to self-heat. The ability to discharge them 100% vs 50% for lead-acid and AGM is a definite bonus. Since budget sounds like a factor here I wouldn't sweat it, but if the money were there I'd be still considering lithium for my aux because you'd essentially get twice the accessory life for the given battery size.