Am using a 1 amp 12 volt SLA battery charger (pushes charge at around 14 volts) to keep 2 extra SLA batteries (wired in parallel) topped off and “fresh”. The charger is a “semi-smart” wall wart charger (starts off at fast charge then slows rate to “trickle” when indicator light shows batteries are charged but is not fully programmable).
The extra SLA batteries I have are currently not in use in any device and were purchased when I got a good deal on a set of 12 for my alarm system and several UPSs I have. I just want to keep the extras in a “storage” state to prolong their lifespan (I accidentally killed a couple of SLAs I had previously when I forgot I had them in storage and allowed them to self discharge too low such that they could not be recharged).
Power to the charger is turned ON and OFF by a Zigbee plug controlled by HE. For those of you in the know, what is the optimal voltage to keep these SLAs charged at to maintain lifespan (I think overcharging sulphinates the plates and dehydrates the gel and undercharging also kills the battery). Also, am I better off charging them very frequently (program HE to charge every other day for 3 min for example, or am I better off charging back to full capacity less frequently, for example once a month or every other month?
I can use a multimeter to measure the resting voltage of the batteries (taken about 2-3 hours after charging them with no load) to figure out how long I should let the charger run depending on the frequency of charging in order to hit the ideal storage voltage (whatever that is).
I am fairly familiar with LiPo battery recommendations (not good to keep them fully charged, and not good to allow discharge below around 65% with ideal storage capacity at around 85%) but do not have a clue about SLA battery recommendations. Any help and recommendations is greatly appreciated. Thanks for any help.
Typical is 2v35 per cell or 14v1 but believe it or not SLA are not all the same depending on discharge capabilities and if they are deep cycle or not. Some charge up to 14v6.
I would really recommend that you check the spec sheet for the battery that you have to get the recommended charge voltage.
Frequency: Typical recommendation for recharging SLA for an electric scooter for instance is every three weeks when in storage. On the other hand I have a deep cycle pack that recommends charging every 6 months. Again the spec of the battery should be referenced.
If in doubt or the info is unavailable, charging to 14v1 every month should be fine. I would not charge more frequently than that.
Edit: Oh and I would let it sit and charge for 8 hours.
Steve,
Thank you so much for your quick reply and insight. I guess part of what confused me is that I thought certain batteries were designed for either float use or cycle use (plate design being different, e.g., float use with thinner and more plates, with deep cycle batteries with thicker, more “resilient” plates). The only specs I found for the batteries in question (12v8A SLA/AGMs) specified Float Use: 13.6-13.8v and Cycle Use: 14.6-14.8v at no more than 2.4A I am ultimately using them in Float Use (backup batteries in case of power failure) but I always thought the plates were designed differently for each type. No specs were given regarding charging frequency recommendations although one site stated that manufacturers generally recommend charging at 70% or when voltage gets to 2.1v/cell, so 12.6v in my case. Again, thanks for your input. People on this forum have been extremely helpful to me.
Ah, you also touched on a point that I did not address since we were just talking about maintenance charging but yes the max charge rate must be obeyed if depletion is sufficient, then the charge voltage must be reduced at the beginning.
