Thor Forums

[Pete'sMH]

Originally Posted by DavidEM

Not much has been said about the type of battery, its construction or its expected life in the above posts. So here goes:

Traditional flooded cell lead acid batteries (the kind with liquid electrolyte inside) need to be specifically built for deep cycle use to get decent life. Deep discharging causes the lead in the plates to be converted to lead sulfate which if left in a discharged state for long, settles out and forms a sludge on the bottom. To combat this, real deep cycle batteries are made with heavier plates that can stand the loss of lead, have more room in the bottom before the sludge builds up and shorts the plates, more headroom above the plates for extra electrolyte and of course filler caps to check and replace lost electrolyte.

Very few 12V batteries are built this way. Your average Walmart, Costco, Batteries Plus, etc are not. Golf cart batteries are built this way because golf cart use is very deep cycle and they will last much longer than your garden variety battery. They are also pretty cheap because the GC market is big and competitive.

There is another type of battery that was mentioned above, the AGM type. These have a glass mat that absorbs the electrolyte and keeps it from being fluid. It won't settle out lead sulfate and seemingly allows the lead sulfate to be more easily converted to lead thus preserving life when used in deep cycle use. They are more expensive but are great for difficult installations because they have no filler caps and don't require checking the electrolyte.

Both of these types of batteries shouldn't be discharged below 50% as that causes lead sulfate to settle out permanently. They also cannot be left in a partially discharged state for long as the same thing occurs.

Carbon foam batteries such as Firefly have a different plate/electrolyte configuration that I don't really understand but they apparently can be discharged deeper and left discharged longer with minimal harm (1,000 cycles at 80% vs 2,000 cycles at 50%).

And then finally there are LiFePO4 batteries such as Battle Borns. They are perfect for deep cycle use as they can be discharged deeply, left in a discharged state for months and can be recharged at high current rates at least double of those above.

So here are some prices for the different types of batteries and are based on approximately 100 nominal amp hours at 12V. It also includes usable amp hours and $/usable amp hour:

GC- $100-125, 60 Ah, $2
AGM- $250, 50 Ah, $5
Firefly- $500, 80 Ah, $6
Lithium- $900, 90 Ah, $10

If you have the room and the weight carrying capacity and you don't mind checking electrolyte and filling with water 3-4 times a year, GC batteries are your best bang for the buck. If you are tight on space and weight then the lithiums might be a good choice, but at a big price differential.

David

Good explanation of the options. But it assumes the buyer needs a maximum performance option. We never boondock and have always found one or two flooded 12V deep cycle batteries to be more than adequate for our needs. If you keep them full and charged they can last 5 years or more. Not bad for $75.