Today I’m going to put forth a very simple question, about Lead Acid Batteries.
Here’s the scenario:
We’re building a solar generator, battery box or some other sort of portable power system. We decided on lead acid batteries for that system. After some measurements and calculations we’ve decided on 100 amp hours for the system. We’ve headed to the battery shop, and picked ourselves up a 100 amp hour AGM.
After building the system and taking it into use, we realize we can only discharge the AGM to a maximum of 50% of its published capacity, before the battery is irreparable damaged.
Question: If a 100 amp hour AGM or lead acid battery can only safely discharge down to 50% of its rated capacity, why isn’t it labelled as a 50 amp hour AGM or lead acid battery?
People who routinely work with solar power systems or portable power of various types, already know of the 50% discharge limitations of lead acid batteries. However, comparisons of AGM or lead acid batteries to other battery chemistries, are still being done with the deception in place.
What is the deception?
The deception is an AGM or Lead Acid will only supply 50% of its rated capacity. It would take two 100 amp-hour hour AGMs in parallel, to get 100 amp hours out of the system.
If we compare a AGM battery rated at 100ah, to lithium iron phosphate pack rated at 100ah, the lithium iron phosphate pack is always going to win in terms of watt hour per ounce or gram. The Lead acid community will counter by saying “but lead acid batteries are cheaper”. This also appears to be a sort of deception, since we actually need two AGM or lead acid batteries, to actually get the desired watt hours out of the system.
Another counterpoint given by the lead-acid community is “the complexity of lithium battery chemistry” as compared to lead acid. Our own stupidity or ignorance shouldn’t be a deterrent to implementing a better battery chemistry in our projects. This goes along with the comment we hear so often in these videos and blog posts ” I shouldn’t need a University degree to charge my battery”. 🤔😀
So in the end, which one is actually cheaper? On my Channel we typically use lithium iron phosphate cells. LiFePO4 cells typically have a cyclic life of 2000 cycles. Keep them in the 20 to 90% charge-discharge range, and their lifespan is extended. Even when they finally start deteriorating, the only affect is reduced capacity.
Bottom line. The lithium iron phosphate cells we use in our battery projects on the channel, may appear to be more expensive when initially purchased. In the long run, especially if we’re building them ourselves, (and even if we’re not), are a far better value, then the typical AGM, deep cycle, or lead acid battery!
Food for thought.