Originally Posted by Sayjac
I have a related question on flooded maintenance free (no caps to pop) vs the maintenance (distilled water can be added) type. All other things being equal or close, and batteries maintained occasionally with a battery maintainer, which type battery is preferable? Or is there no significant difference?
Well keep in mind this is opinion, I'd prefer removble caps so as to be able to check electrolyte density and levels.
The maintenance free battery likely needs higher voltages to reach true full charge. I think the Maintenance free idea, is basically marketing, marketed toards those who immediately think when asked the last time they changed their oil, say 'changed it to what?'
The calcium in the plate paste of MF batteries does lower the offgassing compared to a regular battery, and if the vehicle does not intentionally undercharge the battery, and the driver does not discharge the battery much with engine off playing stereo, then a MF battery could certainly be 'just fine'. I've heard they are marketing marine batteries with maintenance free capless designs, and I think these would make for very poor batteries in an intentionally deeper cycle application and would recommend avoiding these.
BUt the specific vehicles charging system, specifically its voltage regulation, will have huge effects on battery life, likely far more so than the manufacturer of the battery, or its sticker.
While a computerized voltage regulator and one with a hall effect sensor to measure amperage into and out of battery could perfectly recharge a battery to truly full, in theory, those with sensors are more or less present to keep the battery at a low enough level of charge that it can accept higher amperage when the voltage regulator asks for higher voltage. A fully charged battery cannot accept much amperage even at high voltages, but one under 80% charged can.
A 70% charged battery held at 12.8v might only accept an amp or two, but if the voltage regulator immediately wants 14.7v, then that battery might accept 50 to 60 amps before its voltage at the terminals increases to 14.7v, and each 25 amps the alternator makes is said to eat up one HP from the engine. Achiving instant absorption voltage on a discharged battery requires a lot of amperage. the bigger the battery, the more amperage, the healthier the battery, the more amperage, the more discharged thge battery, the more amperage required to instantly bring it up to high absorption voltages.
When New and well discharged my group 27 northstar AGM battery( 930cca, 90Ah) would eat up over 105 amps from my alternator, for several minutes before voltage even hit 14.7v, yet when fully charged it would accept less than 0.4 amps at 14.7. Basically the ammeter is a prerequisite on an AGm battery to determine full, and the ability to bring it to absorption voltage in order to look at the ammeter, as full charged cannot be determines t lesser voltages
A 99% charged battery held at 12.8v might accept 0.1 to 0.5 amps, and if voltage is boosted to 14.7v might only accept 1 to 2 amps.
So one can see how manipulating voltage to keep the battery discharged to the point it can accept larger amperages when the system voltage is increased could have some MPG impacts.
Some Auto manufacturers, certainly not all, have decided to use the battery as a quasi regenerative braking device in an attempt to eek out a few more tenths of a % of MPG, and they do this at the expense of battery longevity as the lead acid battery always wants to be 100% charged or as close as possible to this ideal.
Such vehicles one can do little but occassionally top up the battery with a plug in charger, and get the battery occassionally truly full, the problem is most garage style chargers are afraid to actually fully charge the battery as It is safer to undercharge a battery than overcharge one. The time each battery requires it be held at absorption voltages is different and there is no one size fits ll algorithm. This time varies with different battery temperatures and differs as it ages too.
If one were to dip a turkey baster style glass hydrometer( the plastic EZ red style and its ,clones yield highly inconsistent readings, IME) on a battery whose smart charger has flashed the green light, they will often find the acid density to be only fair, or perhaps even poor.
When a battery has been chronically undercharged it becomes more and more difficult to actually get that electrolyte back upto its maximum. Longer times in the mid to high 14 volt range are required, and after that the equalization charge of 16.2v might be required to actually top out the specific gravity, and bring the battery back to its maximum feasible capacity at that point in its life. Achieving 16.2v is something few chargers will allow, but it stands the best chance of dissolving hardened sulfate back into the electrolyte, and returning the battery to its maximum potential capacity and performance. this does not mean however that a sulfated battery should always be brought to these rather extreme and abusive voltages. As little as required as often as necessary, and thin plate starter batteries have less active material to work with, so the EQ charge on starter batteries should be applied seldomly if at all.
The marine or deep cycle lead acid battery which does not see chronic undercharging, seldom if ever requires EQ charges, but 2 weeks of daily deep cycling and only 85% recharges occurring, then regular 14.7v absorption voltage held for many hours even, stands little chance of reverting the electrolyte back to its maximum, and 16.2v can do in 30 minutes what 24 hours of 14.7v could not and is likely less abusive. If 24 hours of being held at 14.7v cannot do it then weeks of 13.6 or less stands absolutely no chance.
Any charging is better than no charging, but if one really wants to get maximum service life from their battery then it should be occassionally truly topped off. This can be taken to extremes, and batteries are only rented anyway and 'good enough' is a line definable by each individual, and there is certainly bliss in ignorance of battery condition, until the dreaded click click click anyway.
Achieving excellent battery longevity is all about the proper recharging of it, and this is all about voltage regulation. bring the battery to mid 14v range until it is full, then a float or maintenance voltage is held to keep the battery there. The perfect voltages vary with battery temperature and vary slightly with different batteries. How much engine heat the battery is exposed to also has huge effects on longevity as the hotter the sulfuric acid is, the better it is at chewing up the plate paste. A trunk mounted battery regularly topped off by a grid powered charger, in a vehicle that is not trying to use the battery as a quasi regenerative braking device, should last 5 to 8 years easily.
I'm on 6 years on my AGM, and it has over 1000 truly deep cycles on it and many thousands of engine starts. If I could not bring it to and hold it at the proper absorption voltage any time it is less than fully charged, this battery would have been recycled long, long ago.
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