I have been given 3 90Ah 900A AGM batteries in very good condition for free, and since my stock td5 battery from 2002 is as good as dead (only gives around 300A anymore) I want to put 2 of them (or maybe 3 if that is possible??) in my defender.

Now someone told me i can't simply run the 2 batteries in parallel because they are not new ones and the weak one will destroy the other one.
So how is the best way to run them? I use the landy for some heavy winching sometimes, thats why I want to put 2 or 3 in it.

Niels

What happens is the weaker one takes from the stronger one then it reverses and the weaker one becomes the stronger one and compensates. To be honest I run 2 completly different batteries in paralell for about 2 years but they quickly died together and 2 new numax ones were ordered. I fitted a split charge kit but you can get a relay or winch solonoid to link them if your savvy with the electrics

HEAVY DUTY 12 VOLT BATTERY SPLIT CHARGING RELAY 200 AMP | eBay

One of these.