Here’s a frequent question I hear:
I’ve been to three boat shows this fall and have been looking at both AGM and Gel Cell batteries as replacements for the traditional flooded cell batteries in my boat. Are there any pitfalls to making this switch besides price? Which would you choose?
The short answer is, it depends on your boat and how it is currently equipped. But first, a little background.
Both absorbed glass mat (AGM) and Gel batteries are classified by the American Boat & Yacht Council (ABYC) as “immobilized electrolyte” batteries. At a boat show several years ago I saw a guy drilling holes into the case of an AGM battery to demonstrate that nothing would leak out. This is certainly one of the advantages of these battery technologies; no loose acid if the battery case gets cracked. They also promise longer life and no maintenance, which is compelling.
Gel Cells will also offer great performance but they are comparatively finicky when it comes to being recharged. So if you have a standard alternator(s) on your engine(s) with integral voltage regulators for the charging system, every minute you are underway you will be damaging the batteries. Engine-driven alternators are simply not calibrated to provide the best recharge regimen for gel cell batteries.
A shore power-fed battery charger will probably have multi-phase charging capability, but again it must be reset to a gel cell calibration. Most of the newer units allow for this either on or in the unit. On a boat with remote external voltage regulators, calibration of the recharging system makes it possible to cater to the needs of the gel cell.
As for discharging, at least one large manufacturer, East Penn Manufacturing, who makes the DEKA marine brand, has told me that their Gel Cells outlast their AGM batteries in a deep cycle situation. They say this with a caveat, though: that they have to be connected to a properly calibrated charging system.
AGM batteries are proving to be far more forgiving when it comes to charging and discharging. They seem to withstand continued deep-cycling rather well, in spite of what East Penn has told me about their batteries. Again, you’ll want to adjust your onboard battery charger to an AGM calibration if it has one; if it doesn’t, use the “flooded cell” calibration scheme for best results. As for the engine driven alternators with integral voltage regulators? The AGM’s are going to be a better choice than the gel cells. Time in the field has shown they can handle higher regulated voltages and less sophisticated recharge regimens than their gel cell cousins.
— Ed Sherman