Buying all new batteries at the same time?

[Sage]

I'm replacing all my agm batteries in my solar bank. Old age says it's time for new ones, but I can only afford to buy 2 of them right now. I've heard you MUST replace all batteries at the same time. Is there a time frame window that would be acceptable for buying 2 new batteries now and 2 more in a month or two or three? I don't want to ruin my batteries.

 

[Dzl]

I'm replacing all my agm batteries in my solar bank. Old age says it's time for new ones, but I can only afford to buy 2 of them right now. I've heard you MUST replace all batteries at the same time. Is there a time frame window that would be acceptable for buying 2 new batteries now and 2 more in a month or two or three? I don't want to ruin my batteries.

I suspect the type of battery you are talking about might have some effect on the correct answer. (Edit: oops, didn't notice we are in the lead acid subforum)

I also suspect there is no clear point where it goes from acceptable to not acceptable, but the larger the difference in age/wear the more 'mismatched' they will be. I believe there are some good videos on this on youtube, see if the altestore has done any videos on this topic.

This is not an area I have much insight though, sorry.

 

[Steve_S]

I have Lead Acid & LFP so I might be able to help a bit. With FLA/AGM the ruling factor is the weakest battery in the set which brings all the batteries down to its level within the battery bank.

So assuming you have 4 12V batteries, 2 in series, 2 in parallel and you want to replace 2 of the batteries now & 2 later. Check each existing battery for voltage (unfortunately with AGM you cannot check the electrolyte) and if you have a load-tester, test each one "independently" (meaning disconnected from the other batteries) and eliminate the two weakest. Now the weakest of the two remaining will be the common denominator of what you will get out of the whole bank. For short term and NOT severe use, this generally would be ok for 6 months (but no more) because the FLA/AGM will settle to it. * The load tester to use is similar to that used for automotive batteries IF they are 12V AGM, which can give you the cranking amps etc. NAPA here will test batteries for folks....

Something important on current Lead Batteries of all types. A lot of "Brand Labels" are not what they used to be as a result of corporate merger's and buyouts, product quality has gone down for many. Now if you are looking at say Trojan, Full River or other quality Solar AGM Deep cells you should be fine. Be very cautious and look at "CURRENT" reviews as old ones mean squat, If there is a Really Good Deal that too good to pass up, PAUSE and THINK ON IT SERIOUSLY.

Now knowing what capacities you are looking for at what voltage, it's hard to make any suggestions. I should mention that Lifepo4 (LFP) has come down quite considerably, in fact I am replacing my 24V/856AH (428AH @20 net) of Rolls Surette Deep Lead with 24V/910AH (728AH @ 80% use NET) for close to the same cost as my Lead Bank was 5 years ago. (the lead is being repurposed, it's not dead) Now I SCREWED UP when I started by overpaying & buying a ripoff "prebuilt" so that lesson cost me ... BUT had I been smart & DIY'ed it all to start with I'd have been far better ahead of the game.

Hope it helps, Good Luck
Steve

 

[Sage]

I have Lead Acid & LFP so I might be able to help a bit. With FLA/AGM the ruling factor is the weakest battery in the set which brings all the batteries down to its level within the battery bank. For short term and NOT severe use, this generally would be ok for 6 months (but no more) because the FLA/AGM will settle to it.
Something important on current Lead Batteries of all types. A lot of "Brand Labels" are not what they used to be as a result of corporate merger's and buyouts, product quality has gone down for many.

I won't be mixing old and new batteries. I am getting rid of all my old ones and starting fresh. I can run at a diminished capacity for a month or two with only buying half the batteries I eventually want. So I will be buying two new batteries, using them for a month or two, then buying and adding two more identical batteries to bring my system back up to speed. Based on what you said about short term I think I'll be OK. Thanks for the info about new batteries. I won't even consider the "great deals" I'm seeing on off brand batteries. I will be sticking with a tried and true name brand.

 

[Steve_S]

I won't be mixing old and new batteries. I am getting rid of all my old ones and starting fresh. I can run at a diminished capacity for a month or two with only buying half the batteries I eventually want. So I will be buying two new batteries, using them for a month or two, then buying and adding two more identical batteries to bring my system back up to speed. Based on what you said about short term I think I'll be OK. Thanks for the info about new batteries. I won't even consider the "great deals" I'm seeing on off brand batteries. I will be sticking with a tried and true name brand.

It is unfortunate as a lot of "conventional" battery maker's got bought up my large multi-nationals.... The effect has been seen across the automotive industry and beyond . Just be cautious and look for CURRENT reviews & write ups only. Of course you could buy Rolls Surette, Tojan, Full River and so on but they are serious coin for the heavies. I believe that my Rolls S-550 (S6-L16-HC) which are 6V Big FLA are now selling around $400 a pop +/-..

 

[Sage]

Is Mighty Max ML a good brand of battery in your opinion? I want to be sure I'm doing this right. Will a 330 Ah AGM battery bank provide 7 amps continuous power for 4 hours per day for my appliances if I only want to use 30% of my battery capacity every day? Would I have enough battery storage? Are 4 panels enough to recharge a 330 Ah battery bank every day? I have 4, 100 watt, 12 volt panels in parallel that deliver 5.86 amps each.

 

[Trukinbear]

It is unfortunate as a lot of "conventional" battery maker's got bought up my large multi-nationals.... The effect has been seen across the automotive industry and beyond . Just be cautious and look for CURRENT reviews & write ups only. Of course you could buy Rolls Surette, Tojan, Full River and so on but they are serious coin for the heavies. I believe that my Rolls S-550 (S6-L16-HC) which are 6V Big FLA are now selling around $400 a pop +/-..

I'm crazy about my Industrial/Forklift 48V battery - keeping all the nuts tight on all those cables I had with the 32-T105a's make me actually crazy! Dollars per watt I don't think you can do better plus they are rugged beyond belief, and individual cells are replaceable.

 

[Trukinbear]

And yes to answer your question - Try to buy identical batteries all at the same time, all from the same lot if possible. You want everything as identical as you can right down to the length of your cabling. Old batteries plus new batteries soon equal just old batteries... the old ones will suck the life out of the new ones unless the old ones aren't very old.