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bobbolotune's avatar
bobbolotune
Explorer
Apr 28, 2021

How to boost charge AGM batteries in storage?

The manual for my Lifeline 100 Amp Hour Deep Cycle AGM 12 volt batteries says this:

"While in storage, batteries should be boost charged every 90 days or when open circuit voltage drops to 12.5 volts for a 12 volt battery. Boost charge batteries using a constant voltage charger set to 14.4 to 15.0 volts for a 12 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)."

I don't understand this at all. What is a boost charge? What is a constant voltage charger? How do I measure when the charging current falls below 0.5 percent?

So I tried calling the battery technical support, but it didn't help. He said several things. He said a cheap battery charger from Walmart might not be able to get up to the required 14.4 to 15.0 volts. He recommended a specific charger and said there is a boost charge button. He said just press that button and it will do what is needed.

But then I looked up the recommended charger and there is no boost charge button. Rather, it is one of these fully automatic battery chargers with no buttons at all. Also when I got to the 5th review on Amazon saying that this charger overcharged and boiled their AGM batteries I decided to believe it and stay away from this specific charger.

So where do I get a charger with "constant voltage boost charge" capability? Well, he also said that boost charge is just the first stage of a 3 stage charger. So does that mean I can just get any 3 stage charger and it will boost charge the batteries, then harmlessly let it go into the other 2 stages? That actually there isn't any special charger needed?

Also, that the manual says the boost charge should be applied until the charging current falls below 0.5 percent. He said that only high end chargers will say the charging current. Including the specific charger he recommended doesn't have this feature, so he said don't worry about that. I suppose because a smart charger knows when to cut off.

I am still completely lost about what I need to do. Do I need a special charger or will any charger that supports AGM batteries do what is needed? Most battery chargers are completely automatic, so will it automatically do what I need? Maybe the battery manual quote above is only confusing words (saying to use a constant voltage charger set to specific volts) where actually any battery charger will do what is needed?

If someone could even recommend a specific charger, maybe something available on Amazon, that would be greatly appreciated. There are so many battery chargers around it is hard to pick a specific one. My needs are minimal, only to boost charge the batteries while in storage once every 90 days at most, so a low end charger should be enough... if it has the features that are required (and does not have a reputation for boiling AGM batteries).

I am completely lost and hoping someone can help. Thanks!
  • JimK-NY's avatar
    JimK-NY
    Explorer II
    May 01, 2021
    red31 wrote:
    JimK-NY wrote:
    MEXICOWANDERER wrote:
    Maintenance not in use.


    I think I need a Mex to English translator.


    maintenance - not in use, not being discharged, stand by.

    in use - being discharged or used!


    This makes even less sense. I feel like I landed on an alien planet.
  • red31's avatar
    red31
    Explorer
    May 01, 2021
    JimK-NY wrote:
    MEXICOWANDERER wrote:
    Maintenance not in use.


    I think I need a Mex to English translator.


    maintenance - not in use, not being discharged, stand by.

    in use - being discharged or used!
  • JimK-NY's avatar
    JimK-NY
    Explorer II
    May 01, 2021
    MEXICOWANDERER wrote:
    Maintenance not in use.


    I think I need a Mex to English translator.
  • JimK-NY's avatar
    JimK-NY
    Explorer II
    May 01, 2021
    MEXICOWANDERER wrote:
    .........

    Weekly application of temp compensated 14.4 volts constant for 2 hours each would approach ideal numbers. Temp compensation would be important.......


    I use temp compensation. Even so 14.3 or 14.4 nominal volts and 2 hours typically leaves me a long way short of 0.5%. In fact if I start with batteries at about 75%, after bulk, I can hold the absorption for 2 hours and am still pulling about 3% amps. I called Lifeline and discussed this without any resolution or new information. I typically need to maintain 14.3 volts for at least 4 hours to get below 1%. That is with relatively new batteries. Since I am using solar, an interruption with a passing cloud or some shade will greatly prolong the absorption charging time. Sometimes it seems that even a brief interruption results in the need for another hour of absorption charging.

    The whole process just seems weird and exceedingly slow.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Apr 30, 2021
    Using kWh measurement, recharging at less than 20% A/H capacity from 50% level of charge progressively deteriorates the final AH storage capacity of the Lifeline. Like any other electrochemical reaction, the effect is time reactionary. The longer the accumulator stays discharged and the slower the recharge x cumulative number the greater the storage degradation. In effect - my stored 31 would be affected more by slow recharge than a similar unit discharged for a day or week.

    Weekly application of temp compensated 14.4 volts constant for 2 hours each would approach ideal numbers. Temp compensation would be important.

    But for my unit I have decided that 8 hours at 14.4 voltage saturated (constant voltage) would be ideal. The battery may start out at 80 amperes acceptance. Such high amperage in excess of 20.0 (It's a 100 amp hour 31) is not necessary.

    Any arguments against this protocol would have to contain explanation of its service life and ultimate low loss of capacity, please.
  • BFL13's avatar
    BFL13
    Explorer II
    Apr 30, 2021
    http://lifelinebatteries.com/wp-content/uploads/2015/12/6-0101-Rev-E-Lifeline-Technical-Manual.pdf

    Page 20 has the 20% mention but is for deeper than 50% DOD cycling. They do say if you don't have that many amps of a charger, you could use their constant current final stage trick (hard to do with normal charging equipment)

    That is in contrast with Trojan's 20% for all Bulk stage AGM charging (which would have to be under 75% SOC to get any Bulk Stage with a 20% initial charging rate)

    The Lifeline manual does give some times for the Absorption stage, which are not very long, but not clear on the whole profile those times go with seems to me.

    That Lifeline blurb also mentions progressive capacity loss from a series of incomplete recharging like 50-90s when you would get sulphation and then have to do a reconditioning. That desulphation would not harm the battery anywhere near as much as leaving it sulphated IMO.

    In all cases you still need an ammeter to see when you are down to 0.5a/100AH. Your charger or converter can't tell you that. It especially can't tell you that the amps being accepted have started to rise again after tapering! Oops. Stop the recharge! the battery is heating up.
  • MEXICOWANDERER's avatar
    MEXICOWANDERER
    Explorer
    Apr 30, 2021
    This is a key factor in determining whether a 20% of amp hour recharge becomes mandatory...

    AGM batteries tend to demand 20% amperage the further they are discharged.

    For maintenance purposes if power is available try to keep them from 90% to 100%.

    At 50% fill, the 20% rule applies strongly.

    I've noticed with my (6) Lifelines that the greater the amperage seen at a 14.4 volt limit the faster they will pass through the final 5% of charging. Meaning a 50 ampere initial charge rate improves the speed of the final 5% by more than 10% Less time. I haven't measured it because it is a moot point. Recharging a 50% discharged Lifeline slows down the final 5% to an agonizingly slow pace.

    The 20% recharge factor may be one of the top negative issues with absorbed glass mat technology. The final 5% capacity requirement doesn't help it's reputation either. Raising voltage from 14.4 to say 15.0 does not aid much to recover time loss either. It gives me thought of using a wet battery and a DC to DC booster to finish laggard AGMs.
  • JimK-NY's avatar
    JimK-NY
    Explorer II
    Apr 30, 2021
    I talked with Lifeline technical reps in the past. They are used to dealing with returns and issues for older and often neglected batteries. A heavy reconditioning cycle can often restore them for years of use. It seems that the low cost Noco can accomplish a reconditioning cycle.

    I am certainly not an expert but if they were my batteries, I would start by a simple 14.3 complete charge. Then I would do a load test (with 100 watt incandescent bulbs). If the load test looked good, I would not do the reconditioning. Perhaps I am just overly cautious but the reconditioning seems to be harsh and a step for otherwise terminal batteries.

    In any case the OP has a couple of other choices and for the future they could merely get a low cost trickle charger to maintain charge.

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