Forklifts and large submarines have a luxury that unfortunately we cannot afford in PSUBS and that is the use of large volume batteries. An application closer to us is the scooters used in tech diving that are used to explore miles of underwater caves in a given dive. They test their batteries by measuring the various discharge rates of batteries and group similar discharge rated batteries together as they have the same charging rate and do not display the issues described in previous posts. They are tested regularly over their lifetime to insure matched service. When you purchase batteries, you can request that the battery firm provide you with a matched set for a small premium and thus save buying a bunch of batteries and matching them yourself. If you replace one, you have to replace all to keep matched service. R/Jay Respectfully, Jay K. Jeffries Andros Is., Bahamas Vive vt vivas - Live that you may live _____________________________________________ From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Hugh Fulton Sent: Friday, May 09, 2008 18:07 To: personal_submersibles@psubs.org Subject: RE: [PSUBS-MAILIST] uneven charging The best solution, I have been told, is to use 2 volt cells in series. This is how forklifts etc do it as it is very hard to get the internal resistance of batteries to be the same. Forklift batteries generally have 2 volt cells that are up to 2000 Amp-hours per cell. This is why you should always recharge batteries, that are in parallel, in isolation. Also batteries left in parallel can discharge themselves through this unevenness. All this was explained to me by a battery importer. Makes sense to me but I am still going for parallel as the 2volt cells with high amp hours are a crazy size physically. This probably explains some of the problems I have in my boat which has 3 batteries in parallel. It is very common advice in the marine industry that id you are using batteries in parallel you should use the same manufacturer, size and model of battery. Hugh
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