Justkeepitsimple
New Member
Hello everyone. I have (four) 12 Volt 270AH Group 4D deep cycle lead acid batteries.
They’re manufactured by EastPenn (Deka) for NAPA auto parts
NAPA part # BAT 8274
East Penn part # 904D
https://www.napaonline.com/en/p/BAT8274

I bought them back in November in preparation for the final assembly of our off grid solar system. I was able to stack points rewards that were about to expire, some old bulging trash batteries for core credit, and a holiday sale to get a good price and seized the opportunity even though I knew the final assembly of the project would be some months away.
They’ve been stored in a cool dry place out of elements and direct sunlight. But we did have ambient temps +90 fahrenheight for a few months this summer.
When I bought them they all had a resting charge of 12.63- 12.65V (98-100% SOC). I have never charged or discharged them.
Currently they have a resting charge of 12.5 - 12.53V (88-90% SOC).
My question is what is the best way to treat them coming out of storage before final installation in the solar system? I’ve read a lot of the articles on battery university and mined the archived posts here.
This is some information on Lead Acid batteries I’ve gathered:
-For prolonged storage conditions it’s best to remove the electrolyte while fully charged (
didn’t do that unfortunately). Best to store dry because the sulfuric acid electrolyte stratifies. You get a very rich layer of acid toward the bottom of the plates and higher % concentration of purer H20 higher up on the plates which is not ideal when you go to recharge.
-Flooded Lead acid batteries self discharge over time; this rate of self discharge is exacerbated by temperature extremes and electrolyte stratification.
-Lead Acid batteries need a controlled four stage charge cycle (Bulk, Absorption, Float, occasional equalization about every 30 days) To maximize cycle life and maintain maximum capacity.
-Flooded lead acid batteries ideal charge rate (for Bulk and Absorption stages) is 0.1 C of their total rated current. A good battery charger/ solar charge controller will taper back significantly and progressively to top off the final 10-15% at a lower C rate (0.05 to 0.01C) until reaching 100% SOC and holding float voltage.
-For battery life size system for a minimum 10% depth of depletion to a maximum 50% DOD when sizing overnight load requirements.
The design philosophy I implemented when designing they system was essentially to power our chest freezer and devices <500w continuous daytime only. Taper back to essential loads (lighting, Starlink router, and device chargers <300w conservatively, for about 4 hours after sunset. Inverter shut down at bedtime. According to my calculations this will keep our overnight consumption to less than 10% DOD on the battery bank. I really want to maximize the longevity and utility of our battery bank.
System is 12 volt
-1000 watts of solar panels feeding solar charge controller
-SCC Is Morning star Tri star MPPT 60AMP (800W max output to battery bank @12 volt)
-Battery bank is the (4) 12 V 270aH flooded lead acid batteries
-Inverter is Morningstar SureSine 12V 700W inverter
-Cloudy day/ overnight top off battery charger is 12 Volt 55AMP IOTA with 4 stage charging algorithm
I am thinking to hook up two of the four batteries in parallel at a time (540 Ah) and give them a full charge cycle from the IOTA 12V 55AMP battery charger before hooking them up together (~0.101 C rate) on the SCC bus bar to give them a full capacity start. Once the whole bank is fully charged then the 60AMP solar charge controller should give them a 0.05C rate which should be enough to keep them charged up after nighttime 10% DOD and run daytime loads.
I can’t emphasize enough that I designed and plan to utilize the solar system/ battery bank to not cycle down more than 10-15% DOD at a time. From what information I’ve gathered that will get me the maximum cycle to capacity to longevity utility out of it.
I’m pretty sure I should fully charge the batteries before I hook them up on their maiden journey in the completed system?
Should I attempt to “stir” the electrolyte before I recharge the batteries?
Should I run an equalization cycle on them since they’ve been sitting for so long?
Obviously make sure they’re all topped off with distilled water.
Long post. Thanks for reading and input- knowledge building. I started with essentially zero solar knowledge 9 months ago and thanks to the lot of archived posts on this forum and people answering my questions along the way. I’ve learned a lot and really want to optimize our solar system for longevity and utility.
They’re manufactured by EastPenn (Deka) for NAPA auto parts
NAPA part # BAT 8274
East Penn part # 904D
https://www.napaonline.com/en/p/BAT8274

I bought them back in November in preparation for the final assembly of our off grid solar system. I was able to stack points rewards that were about to expire, some old bulging trash batteries for core credit, and a holiday sale to get a good price and seized the opportunity even though I knew the final assembly of the project would be some months away.
They’ve been stored in a cool dry place out of elements and direct sunlight. But we did have ambient temps +90 fahrenheight for a few months this summer.
When I bought them they all had a resting charge of 12.63- 12.65V (98-100% SOC). I have never charged or discharged them.
Currently they have a resting charge of 12.5 - 12.53V (88-90% SOC).
My question is what is the best way to treat them coming out of storage before final installation in the solar system? I’ve read a lot of the articles on battery university and mined the archived posts here.
This is some information on Lead Acid batteries I’ve gathered:
-For prolonged storage conditions it’s best to remove the electrolyte while fully charged (

-Flooded Lead acid batteries self discharge over time; this rate of self discharge is exacerbated by temperature extremes and electrolyte stratification.
-Lead Acid batteries need a controlled four stage charge cycle (Bulk, Absorption, Float, occasional equalization about every 30 days) To maximize cycle life and maintain maximum capacity.
-Flooded lead acid batteries ideal charge rate (for Bulk and Absorption stages) is 0.1 C of their total rated current. A good battery charger/ solar charge controller will taper back significantly and progressively to top off the final 10-15% at a lower C rate (0.05 to 0.01C) until reaching 100% SOC and holding float voltage.
-For battery life size system for a minimum 10% depth of depletion to a maximum 50% DOD when sizing overnight load requirements.
The design philosophy I implemented when designing they system was essentially to power our chest freezer and devices <500w continuous daytime only. Taper back to essential loads (lighting, Starlink router, and device chargers <300w conservatively, for about 4 hours after sunset. Inverter shut down at bedtime. According to my calculations this will keep our overnight consumption to less than 10% DOD on the battery bank. I really want to maximize the longevity and utility of our battery bank.
System is 12 volt
-1000 watts of solar panels feeding solar charge controller
-SCC Is Morning star Tri star MPPT 60AMP (800W max output to battery bank @12 volt)
-Battery bank is the (4) 12 V 270aH flooded lead acid batteries
-Inverter is Morningstar SureSine 12V 700W inverter
-Cloudy day/ overnight top off battery charger is 12 Volt 55AMP IOTA with 4 stage charging algorithm
I am thinking to hook up two of the four batteries in parallel at a time (540 Ah) and give them a full charge cycle from the IOTA 12V 55AMP battery charger before hooking them up together (~0.101 C rate) on the SCC bus bar to give them a full capacity start. Once the whole bank is fully charged then the 60AMP solar charge controller should give them a 0.05C rate which should be enough to keep them charged up after nighttime 10% DOD and run daytime loads.
I can’t emphasize enough that I designed and plan to utilize the solar system/ battery bank to not cycle down more than 10-15% DOD at a time. From what information I’ve gathered that will get me the maximum cycle to capacity to longevity utility out of it.
I’m pretty sure I should fully charge the batteries before I hook them up on their maiden journey in the completed system?
Should I attempt to “stir” the electrolyte before I recharge the batteries?
Should I run an equalization cycle on them since they’ve been sitting for so long?
Obviously make sure they’re all topped off with distilled water.
Long post. Thanks for reading and input- knowledge building. I started with essentially zero solar knowledge 9 months ago and thanks to the lot of archived posts on this forum and people answering my questions along the way. I’ve learned a lot and really want to optimize our solar system for longevity and utility.
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