NEW BATTERY MONITOR: Mastervolt BTM-III

Some of you may be wondering what happened with that battery problem I was having.  As I mentioned briefly, I was hoping the crazy readings I was getting from my battery monitor were the result of a bad connection or some corrosion somewhere.

Back in the 1990s when I was cruising full time and living aboard Crazy Horse, my electrical system was dirt simple. I had two 100-AH wet-cell batteries, a battery selector switch, and a 30-watt flexible solar panel to help keep them topped up. When I wanted to know how the batteries were doing, I whipped out my multimeter and put the leads on the battery terminals to read the surface voltage. For more sophisticated analysis, I used a big eye-dropper hydrometer to test the specific gravity of the electrolyte solution in the battery cells.

The electrical system on my next boat, Sophie, a Golden Hind 31, was just as primitive and my monitoring regimen was much the same. As you can imagine, I thought I’d died and gone to heaven when I obtained Lunacy and finally got to experience something more modern and up-to-date. She came equipped with a Heart Interface inverter/charger with a matching Link 2000 control pad that not only controls the charger and inverter, but also monitors both the (rather large) house battery bank and the separate (rather small) engine-cranking bank, providing detailed data as to surface voltage, amperage flowing in or out, and total available amp-hour capacity. Twenty years earlier (back when I was still playing with my eye-dropper and multimeter on the Alberg), this had been state-of the-art technology and Heart Interface kit (produced by a small independent company, Cruising Equipment Co., based in Seattle) was what every savvy cruiser craved.

I reveled in all the information offered by my Link 2000 monitor for several years, until this year, when said information suddenly became very dark and grim. The monitor continually displayed “Low Battery” warnings for both banks, showed their respective amp-hour capacities as being sorely depleted, and constantly measured amperage flowing out of the batteries, even when there was no load on them. Even worse, negative amperage readings persisted when the batteries were fed power from any and all sources (wind/solar, engine alternator and shore connection). The only normal readings were for voltage, which I easily confirmed with my old friend the multimeter. (I did also confirm that the unit’s charger and inverter controls are still functional.)

As I mentioned before, it seemed either all the batteries on the boat had abruptly died and gone to heaven themselves, for no apparent reason, OR the battery monitor had gone insane. I discussed this situation with Jeff Stack at Maine Yacht Center, and he agreed the latter scenario was much more likely. Indeed, he allowed as how in the past year or so he had seen several formerly reliable 90s-vintage Heart Interface monitors suddenly go tits up. It seems these once popular units may be just now hitting the wall when it comes to life expectancy.

I asked Jeff to look into my electrical system, and he quickly confirmed that my batteries were fine. Unfortunately, however, there were no bad connections or corrosion to explain the monitor’s misbehavior. Not too surprisingly, there is now no support for old Heart Interface gear, as the old company has been consumed more than once by bigger ones. So I had little choice to pony up for a brand new monitor.

The current leader of the pack in this corner of the market is Mastervolt, a Dutch company that produces a vast array of marine electrical kit. I checked out their Masterlink BTM-III battery monitor (see photo up top) and decided it would suit my purposes quite nicely. Though it has many fewer buttons than my old Link 2000 monitor, it is actually quite a bit more sophisticated.

For one thing, the BTM-III can monitor three different battery banks, though one (the primary house bank) is monitored in more detail than the others. Like the Link 2000, the BTM-III can tell you how many amps are flowing into or out of a battery, how many amp-hours have been consumed, and how long a battery can feed a given load before running dangerously low on juice. It can also, however, provide oodles of interesting “historical” information: time elapsed since the battery was last fully charged; time elapsed since the last “low battery” alarm; total number of discharge-recharge cycles; number of “abusive” cycles; total number of hours the battery has spent discharged below 20 percent; total amp-hours consumed; average depth of discharge; deepest discharge; and highest recorded voltage.

With this kind of data, I expect I’ll be able to write a very melodramatic biography about my batteries. Soon to be followed by a major motion picture, action figures, and all the rest.

One interesting note: I can’t just toss the old Link 2000 unit, as still I need it to control my inverter/charger. (Either that, or toss out a perfectly good charger.) So now the two monitors are mounted side-by-side on my distribution panel—one of them spewing nonsense and defaming my poor batteries, the other providing a sober and reliable account of their doings.