Apart from the pros and cons of gel, agm, and open or sealed lead acid batteries, there is a simple truth for all types of battery: the performance and service life is very much affected by the time that passes between its date of manufacturing (or activation) and its first use on the boat. Some types and brands hold up better to the delays in storage and transportation, it’s true, but no battery is impervious to sitting around unused for many months.
If you can find a supplier who sells lots of batteries of the type that you want, there is a good chance that you will get good, fresh batteries. If you are not sure that the supplier has a healthy turnover in the type of marine batteries that you need, it may be better to find a retailer who will order new batteries for you. Unfortunately, neither you nor your retailer can be sure of how long ago the batteries were manufactured in either case.
The result may be that one or more of your new batteries will effectively neither take nor give much of a charge but will just “free-wheel” up and down, along with the voltage of the battery bank.
Unless you know exactly what to expect from your total bank or start measuring, you may not even spot the problem.
Spotting poor battery performance: In a parallel configuration of four or more batteries, one or more poorly-performing batteries may not be spotted until it’s too late, usually when the performance of the remaining batteries starts to diminish. For meaningful measurements, at least an accurate digital voltmeter and a good clip-on digital DC am-meter are required.
User manual: You get a user manual with just about any piece of gear over $10 but you get zilch when you buy your batteries. Never fear: you can find out all about your batteries on the internet. Did you try the Exide website? (Bring lunch.) The odd sticker on e.g. a gel battery will typically say that this battery should be charged by 14.1-14.4 volts. Nasty… If you charge your gel battery for any length of time at 14.4 volts at a battery temperature of say 32C, you’ll destroy it before the month is out. Correct would be to inform the customer that a gel battery requires 14.25 volts at 25 Centigrade to achieve a full charge and a reduction of five milli-volts per cell per grade Centigrade, i.e. to 14.0 volts at 33C (actual values for Sonneschein gel batteries).
No “sell by” date: “Sell by” labels are stuck on any two dollar item but manufacturers do not inform the consumer, who often pays well over a thousand dollars to renew his marine batteries, of the manufacturing or “sell by” date.An indelible manufacturers’ mark would of course enable any retailer to see what they are getting and selling, and any customer to see what they are buying. Most batteries have no indication of their manufacturing date—some brands encode this information, like “UBK” or ”EPL”. Care to guess what year and month that is?
Away from home: In the US and in Europe the date of sale, as indicated on the battery and/or invoice, can usually be used for warranty claims by the customer. However, outside of these areas, the buyer may be on his/her own. Local retailers may balk at accepting any dud batteries because claiming a refund from their wholesalers, mostly located in the US and Europe, is difficult and expensive. Check the warranty conditions before deciding what the best price is!
Next month: Part Two—What you can do
John van Logchem is an electrical engineer reporting from Bonaire who has owned and sailed Queen of Hearts, a Swan 47, since 1992.