Oliver, I can't find the chart of battery voltage vs. state-of-charge at the moment, but in general, it's recommended that you never let the battery get below 50% state of charge if you want maximum life from it. I've seen 2 voltages for 50%, 12.1 and 12.3. A fully-charged battery will read 12.6, if it doesn't, it's junk. You can tell when a lead-acid battery is fully charged by either checking with a hydrometer (the readings will quit rising) or watching the electrolyte in the cells. When ALL CELLS are gassing freely (not 'boiling', just a good steady stream of bubbles), the battery is fully charged. Leave it sit for 24 hours with nothing causing a drain, then measure the voltage. All readings must be taken after AT LEAST several hours of 'rest', no charging or discharging taking place. A period of 24 hours is best. Note that because of the very small difference between voltage readings, an analog meter or the bank of lights in a typical RV is totally useless, a good DVM is mandatory. One of the places I checked in trying to find that chart was http://www.amplepower.com. They have "Killing Batteries" in their technical section, and I took the liberty of copying it here. They sell 2 books, "Wiring 12 Volts for Ample Power" and "Living on 12 Volts with Ample Power", full descriptions and ordering info is on their web site. Both are somewhat general, aimed at not only RVers, but boaters and owners of remote cabins. They have extensive info on their web site on batteries, chargers, and design considerations. Where it says, "ferroresonant charger" in the list below, read that as "UniVolt". <<Jim>> ---------------------------------------------------------------------------------------------------------- Killing Batteries There are many ways to kill batteries ...even very expensive batteries. Below are a few ways to treat batteries ...NOT! Overcharge the battery by applying a voltage above 13.8 Volts for extended period Undercharge the battery by never charging it beyond 13.8 Volts. Discharge the battery and leave it that way for a few days or weeks. Let the battery sit unattended without charging for 3 weeks or longer. Repeatedly discharge the battery beyond the optimum 50%. Slosh the battery around when it is deeply discharged. Boil enough electrolyte from the battery that the plates are exposed to air. Periodically add more acid, or unpure water. Use a ferroresonant charger in a liveaboard situation. Sock the battery with a high output alternator that produces more than 40% of the Ah capacity of the battery. Mount the battery where it regularly gets above F. Charge it hot until you can't even touch the case anymore. Use a big inverter on a small battery and run the inverter until it cuts out from low voltage. Freeze the battery in a discharged state. Use a starter battery in a deep cycle application. Ample Power products are manufactured by Ample Technology, 2442 NW Market St., #43, Seattle, WA 98107 - USA ----------------------------------------------------------------------------------------------------------- Carol and Oliver Filippi wrote: > > Several months ago there was a discussion as to how to determine the charge > level of a lead-acid storage battery by measuring the voltage across the > terminals with an accurate volt meter. > > I failed to archive the info, and now could really use it - especially with > the "modern" maintenance free batteries which do not provide access for the > old standby hydrometer. > > So, please advise as to voltage readings and the charge levels they > represent. Also, any tips on when or how to take the readings in order to > get a good indication of the charge level of the battery. > > This time I will be sure to archive the info! > > Oliver Filippi > [EMAIL PROTECTED] > > To unsubscribe or to change to a daily Digest, please go to > http://www.airstream.net/vaclist/listoffice.html > > If replying back to this message, please delete all the unnecessary original > text from your reply. > > -- <<http://www.oldengine.org/members/jdunmyer>> <<[EMAIL PROTECTED]>> <<lower SE Michigan, USA>> <<mailto:[EMAIL PROTECTED]>> To unsubscribe or to change to a daily Digest, please go to http://www.airstream.net/vaclist/listoffice.html If replying back to this message, please delete all the unnecessary original text from your reply.
