Originally Posted by email@example.com
Im about to store my 95 roadTrek and usually I take out the shore batteries (2 of them) and the main battery in the engine and place them on a trickle charger.
My question is if I just leave every battery in place and plug in the trek to an outlet will it charge my batteries?? or should I take them all out and have them on a trickle charger?
This is question that comes up often, along with the related issue of if full time float or trickle charging is needed or best to use, compared to let sit/recharge periodically.
Here is what Lifeline says about storage of their AGM batteries
While in storage, batteries should be boost charged every 90 days or when the open circuit voltage (OCV) drops to 12.5 volts for a 12-volt battery (6.25 volts for a 6-volt battery and 2.08 volts for a 2V battery). This OCV corresponds to approximately 75% state of charge. Boost charge batteries using a constant voltage charger set at 14.4 to 15.0 volts for a 12-volt battery(7.2 to 7.5 volts for a 6-volt battery and 2.40 to 2.50 for a 2 volt battery). The boost charge should be applied until the charging current falls below 0.5 percent of the battery’s 20 hour rated capacity (0.5 amps for a 100 Ah battery).
And here is what Trojan says about their wet and AGM batteries
The following tips will help ensure that your batteries emerge from storage in good condition:îCharge batteries before placing them in storage.îStore in a cool and dry location, protected from the elements.îDisconnect from equipment to eliminate potential parasitic loads that may discharge the battery.îBatteries gradually self-discharge during transit and storage, so monitor the specific gravity or open-circuit voltage of flooded batteries every 4 - 6 weeks. Monitor the open circuit voltage for AGM or gel batteries every 2 - 3 months. îBatteries in storage should be charged when they decline to the following state of charge (SOC):o Flooded batteries: 70% SOCo AGM/gel batteries: 75% SOC
I think the recommendations are likely pretty good, but don't address whether full time float would be better.
Most AGMs are rated to self discharge at 1-3% a month, so would not ever get to the 75% SOC in 6 months of the recommendations. Lifeline does put in the 90 day limit for no recharge, though, so wouldn't make that.
Wet cells are rated at 5-10% per month so would get there in 6 months.
I do think the time they spend in a discharged state may cause some damage if they go as long a 6 months, but it is really hard to guess how much risk there is.
All the manufacturers have a general recharging rule they want you to follow that is basically you need to recharge a battery as soon as possible after discharging it. The storage recommendations don't follow that rule so that is a conflict. How long you have after discharging before the sulfates start to harden and get impossible to convert back at charging has not been definitively agreed on, though, from what I have seen. Most do put the time much shorter than 3-6 months, though, usually at maybe a week or so.
Since self discharge is continuous, you have sliding scale of how long any amount of your discharge has been sitting. At the end of 6 months, you would have the first 1-3% having sat for 6 months and the last 1-3% only one month. If the recharge quickly or lose the capacity recommendation is correct, you would lose some capacity in storage, especially in the capacity that had been discharged the longest.
I think this may be why some chargers do a continuous float, but then do a full voltage charge for a short time periodically, to maintain that slight amount of overcharge capacity that is between float voltage and absorption.
I normally float ours over the winter, and since we store at home in a heated shop I can get to it all the time, I will occasionally run a 20% discharge/recharge to .5%C amps cycle on it. Probably do that cycle 3-4 times over a winter. I think this covers most angles, but have no proof of it being best.
If I had to guess at an order of best storage, based on mostly what sounds logical. Better first.
*Float with occasional full voltage boost
*Uncharged for 2-3 weeks and recharged
*Same as previous with more time between charges up to the full 6 months of storage
As with all of the charging stuff, getting a known full charge at the end of storage would be essential. With wet cells, doing an equalization would certainly help reverse any capacity loss that happened while sitting.
Most of the smart chargers will not get you a full charge consistently, so having a monitor will tell you if do, and if not completely full a long drive to top off on the alternator may be in order.
For those that have battery monitors, you can get an indirect idea if the storage has caused any degradation of the batteries, but it is not as accurate as doing a capacity test. Get the batteries full to your transition amps setting, let float for 2-3 days and check the amps. If that amp reading is higher than it was with the same procedure done before storage, you have gotten some unknown amount of degradation over storage.
It is very difficult to know if there is anything bad happening from storage as the batteries will almost never be too low to function after 6 months and the losses per storage are not going to be very large if they do happen, with worst cases maybe 5-10% of capacity, and usually less than that, I think. Nobody does capacity tests, so unless you were right on the edge of capacity for your use patterns, you would not know anything happened.