As the owner of two Corbin Sparrows with Optimas which are used daily (10-40 miles typically), perhaps I might offer a few comments.
First off, I agree that individual charging of each 12v battery in a string is mandatory. I've been appalled at the individual battery voltage variation of my Sparrow's 156v pack when using the Zivan for charging the string: as the entire pack voltage climbs over 180v during charging, some batteries approach or exceed 15v whereas others are still at 13.x volts. My battery monitor is a PakTrakr in each vehicle, but I've made a separate calibration chart as its readings can be off by as much as 0.3v.
It's my opinion that the Sparrow's Optima battery bad reputation stems from the fact that the unmonitored batteries had been inadvertently murdered by the charger!
My solution to this dilemma is simplistic:
1. When using any charger, I do so through a simple mechanical timer which I pre-set based on the DOD (in this case, number of miles driven). This is my coarse protection.
2. In each of the two cars I know which battery in the string will attain full charge first and whose voltage will then climb inordinately. When bulk charging with the Zivan I monitor this battery using a voltmeter with an overvoltage alarm. I use this alarm output to open up a latching relay through which the 115vac goes to the Zivan, thus shutting down the Zivan as soon as that battery's voltage hits 15v (I'm still experimenting with the exact setting, as Optimas can supposedly sustain up to 15.6v). At this point the pack is probably around 90% charged, but unbalanced. This is adeaquate when I'm "opportunity charging" away from home.
3. At home, after the above bulk charge, I now finish the charging by disconnecting the (disabled) Zivan and simply plugging in the small smart float chargers attached to each battery: each one charges at 14.7v until the current drops to around 300ma and then kicks into float at 13.7v. I have all these 13 small (and cheap) chargers hard-wired in a 115vac daisy-chain and thus simply have one 115vac under-hood connector to plug in (always through a timer).
Finally, I've also added an Anderson connector pair through a fuse to each battery to enable monitoring or charging each battery individually. Oh, and when charging I open up the hood and take out the seat to provide maximum ventilation for the battery compartments.
I never ever leave the batteries in a discharged state, and recharge them immediately after use.
Obligatory electric-boat content: I'm waiting for one of my two Yamaha 9.9HiThrusts to die so I can replace it with a Torqeedo 4.0R on my catamaran, thus having a 'hybrid' :-)
BTW, I drove one of my Sparrows for two years at reduced voltage (72v) using Deka Gel cells fed by individual smart 12A chargers - the batteries are still in great shape despite the repeated >80%DOD abuse, and I intend to use some of them to power the Torqeedo. It's my understanding that Gels are more tolerant than AGMs for deep-discharge applications, but have a higher internal resistance and thus don't have the AGM's high peak-current capabilities.
Yes, I'll be converting to Lithium- all it takes is time and more money...
FWIW. JoeS.
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