Deep recycled older 12 volt battery showing 13.1 volts after recharge & 22 hours rest. Time to bin it?

[PlacidoD]

I put a new 105 Ah leisure battery in the MoHo last year and have topped up the old under-performing 80 Ah battery occasionally since as I hate waste. While I have the driver's seat off (It is absolute pain to dismount it!) I was toying with the idea of doubling up and putting the old battery back after a deep recycle over the last couple of days. The old battery was showing 13.8 volts off the terminals just a couple of hours after disconnection yesterday and is now showing 13.1 volts after circa 22 hours. Am I wasting my time and effort. Van is is in for an MOT and service tomorrow a.m so the seat has to go back on in the next couple of hours!!

P.S. The old battery may have been underperforming as the mains charger on the van perhaps was not charging it properly

 

[TerryL]

The Old battery will pull down the performance of the new one. I wouldn’t risk it given the aggro of changing it.
But you've probably done it by now.

 

[AdrianChen]

I put a new 105 Ah leisure battery in the MoHo last year and have topped up the old under-performing 80 Ah battery occasionally since as I hate waste. While I have the driver's seat off (It is absolute pain to dismount it!) I was toying with the idea of doubling up and putting the old battery back after a deep recycle over the last couple of days. The old battery was showing 13.8 volts off the terminals just a couple of hours after disconnection yesterday and is now showing 13.1 volts after circa 22 hours. Am I wasting my time and effort. Van is is in for an MOT and service tomorrow a.m so the seat has to go back on in the next couple of hours!!

P.S. The old battery may have been underperforming as the mains charger on the van perhaps was not charging it properly

The battery at 13.1 volts at rest isn't a bad result, but it's not the whole story I'm afraid. If you were to connect a 4amp 12v bulb, in theory the bulb should work for 20hours if the battery still has 80AH capacity, but very likely it doesn't, so may well be much less if its old, perhaps only 50 or even less. So I would asses the remaining capacity first.

Many folk continue to use a battery well beyond the industries mantra that a battery is considered spent once the capacity drops to less than 80% of the sticker capacity, because if you are regularly on EHU, the battery doesn't have to do much, so the user doesn't notice until one day when there is no EHU and the lights go off well before you expect. Capacity checks are a bit tedious......

If both are the same chemistry ie gel agm or flooded they may well play well together, but if the newer 105 you have fitted is for example agm, and the old one flooded, then you have to undercharge the AGM, or badly overcharge the old, which isn't great.

What will happen over time is the newer battery will spend some of it's potential lifespan supporting the old battery, so all will seem well, but you may be a little dissapointed with the lifespan of the new battery, that may be fine if they both last a reasonable time though.

Personally I would check the old ones capacity/chemistry and unless its adding a worthwhile amount, flog it to a scrappie, and get another of the type you've already added.....

 

[Lenny HB]

Change the battery in your multimeter the meter wil read high if the battery is low.
Then see what readings you get.

 

[pappajohn]

As above
I was getting a reading of 16v from a car battery.
new 9v battery in meter and getting 12.7v from same battery

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[AdrianChen]

Thats more realistic - 12.7v is a reasonable resting voltage....

 

[PlacidoD]

Thanks guys! Driver's seat is back on. I decided not to risk it for the reasons you identify.

Next stop after MOT and service tomorrow is to get the passenger seat off and have an explore under there. I am not sure that the mains charger is working properly. I thought it was when on EHU on the drive (The on/off toggle switch certainly works) but it looks to have been solar that was topping up the leisure battery over the winter not the mains charger (and that seems to prioritise the engine battery). My first thought was that I had a parasitic drain on the circuit but it was noticeably worse in the shortest daylight months.

I have now got Optimate 4 connectors directly on the leisure battery so I can be sure I am getting an optimal charge while I tinker with the mains charger under the passenger seat. I want to photograph everything under there and find manuals for it all. (And also measure up so as I am in the know if looking for replacements/upgrades.) I wish I was more knowledgeable about 12 v electrics!

P.S. No way do I want another van with all the leisure electrics under the seats. That is royal pain!! Even the fixings are different on different seat bolts bolts (both Allen and Star heads!) and the seats weigh a ton, remain attached to the seat belts and are difficult to relocate on the studs when repositioning.