Second battery size

[bryco]

Im currently running an optima yellow top 55ah battery only and my intention was to put another beside it in the battery box of the defender.
The thing is that now im thinking i want a bit more juice but i still want to keep the batteries in that same spot. I've found other brands of sealed batteries that are bigger but would still fit in with the optima but i recently read somewhere that you should try to keep the batteries similar in capacity. Any truth in this?
If so how much bigger could i safely go?
Thanks!
Bryco

Sent from my GT-I9505 using AULRO mobile app

[DiscoMick]

Depends what you want to do, where it is and if its to be used for starting. If its in the battery box of the Defender and you use lead acid inside the vehicle it will have to be vented to the outside as they release fumes. Starting batteries are different to deep cycle batteries. 55ah sounds a bit small for starting. My Defender has an 80ah lead acid starter under the passenger's front seat which is vented to underneath the vehicle. Maybe it might be simpler to just get a bigger starter rather then trying to squeeze two batteries into that space. But if you want to run a fridge off the second battery you need deep cycle. For example, to run our Engel 40 litre fridge I just bought a 110 amp AGM which was pricey at $339 but is fully sealed so it doesn't need venting and can handle being deeply discharged. But the AGM wouldn't fit in the battery box plus the starter as I also have the dual battery controller in there. It will go in an Ark box in the back.

Sent from my GT-P5210 using AULRO mobile app

[PhilipA]

If so how much bigger could i safely go?
I have always had different battery sizes for the last 20 years or so with no ill effects.
I currently have a Blue top 750CCA Optima for starting and a 130AH AGM as house battery in my D2 TD5.
They have been in 2 years so far. The Optima is next to the turbo, so it will be interesting to see how long it lasts.

I have not had super long lives from batteries as they have always been in the engine bay, averaging about 3.5 years, although I tend to be conservative as there is no use having a battery to run the fridge if it has only 60% capacity left. You should have no such problems in a Defender under the seat is cool.

My memorable problems have been AFAIK heat with a Optima yellow top, which was still going strong but leaking acid from a terminal, physical failure in a Supercharge where a cell dropped presumably from rough roads.

IMHO the most important issue is keeping them fully charged with a charger if the car is not used daily, and probably to have batteries of the same type eg AGM both so that the voltage characteristics are similar.
Regards Philip A

[incisor]

A turbo blanket makes a big difference and they are not that expensive

[PhilipA]

A turbo blanket makes a big difference and they are not that expensive

Yes I guess I should have added that I have made a stainless heat barrier between the turbo heat shield and the battery which I covered with ALDI reflective aluminium tape and also a battery blanket heat reflector with an air gap between the battery and the extra heat shield.

It would probably still get warm there. That is one reason apart from the CCA density of the Optima . Optimas are supposed to have a greater heat tolerance than other AGMs.

I have also polished the outside of the turbo heat shield and when I can be fussed will polish the inside , which is more important.

Regards Philip A