3 Onboard Batteries

[Carslil Jim]

Hi,
I have a 60Amp alternator and two batteries, one is dedicated to starting the engine, the other is a deep cycle battery (for the fridge). I can switch between the two, or run off both at the same time.

i want to add another deep cycle, which we will be able to isolate, but it will be wired on to the existing deep cycle. The plan is to have heavy cable run to an Andersen plug that can be disconnected. At night the battery will be removed to a friends tent to power his CPAP machine.

What is yr opinion on whether the alternator will be able to recharge the two deep cycles with approximately 6 hours running per day.

[Robmacca]

I'm no expert but I would say no good, I would upgrade to a 100amp Alt at least. It all depends on how low u drain your batteries as well, but 6hrs drive time will not be enough time to charge them up to near full capacity or close to it anyhow...

[Homestar]

Say you drag 50% from each battery, which is about the max you’ll get - so 100Ah. If your alternator is supplying say 10 amps to run the car - no lights, wipers, heater fan, etc then theoretically you’ll have 50 amps up your sleeve. So that’s 2 hours, but I reality, they won’t accept a charge like that and I would say you’d need close to 6 hours to get them full again, but that’s on heavy use.

I ran 200Ah in my 101 for some time - and that’s got a 35 amp alternator in it. I could hear it whine like a bitch when the batteries were low but it always got them full again after a good run.

I’d go for it, I think you’d be fine under most conditions. If not, you can always remove one or upgrade your alternator.