This is from "The 12 volt side of life"
Most flooded batteries should be charged at no more than the "C/10" rate for any sustained period. "C/10" is the battery capacity in amp/hours divided by 10. For a 220 AH battery, this would equal 22 Amps. Charging at 15.5 volts will give you a 100% charge on Lead-Acid batteries. Note that flooded batteries MUST bubble (gas) somewhat to ensure a full charge, and to mix the electrolyte. Float voltage for Lead-Acid batteries should be about 2.15 to 2.23 volts per cell, or about 12.9-13.4 volts for a 12 volt battery. Flooded battery life can be extended if an equalizing charge is applied every 10 to 40 days. This is a charge that is about 10% higher than normal full charge voltage, and is applied for about 2 to 16 hours. This makes sure that all the cells are equally charged, and the gas bubbles mix the electrolyte. If the liquid in standard wet cells is not mixed, the electrolyte becomes "stratified". You can have very strong solution at the top, and very weak at the bottom of the cell.
So you ask: "what does all that mean?" It means that battery charging is a little more complicated than most people think. It's not really safe to assume that driving your motorhome will keep your house batteries up to par, or that plugging your trailer in to A/C power and letting the converter run will make everything hunky-dory. The truth is, most of the RVs on the road have very poorly designed battery charging systems courtesy of the factory. Why? Well, cost plays a key role in deciding what equipment a RV will have installed when it's sold. Most RVs depend on the 12volt converter to charge the house batteries. In most cases, that's a very poor compromise!
The life of your batteries will be longer and happier if you charge them correctly. The best chargers on the market are 3-stage chargers. Use of a good quality 3 stage charger will significantly improve your battery's performance and lifespan. These chargers can be purchased separately or are included as part of many of the better quality inverters. When using a 3 stage charger, battery charging takes place in 3 basic stages: Bulk, Absorption, and Float.
Bulk Charge - The first stage of 3-stage battery charging. Current is sent to batteries at the maximum safe rate they will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage typically range from 10.5 volts to 15 volts. There is no "correct" voltage for bulk charging, but there may be limits on the maximum current that the battery and/or wiring can take.
Absorption Charge: The 2nd stage of 3-stage battery charging. Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage. Voltages at this stage are typically around 14.2 to 15.5 volts.
Float Charge: The 3rd stage of 3-stage battery charging. After batteries reach full charge, charging voltage is reduced to a lower level (typically 12.8 to 13.2 volts) to reduce gassing and prolong battery life. This is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging.
I actually also dont want a cheesy RV of any sort connected to my space ship quality $55,000 tow vehicle. Just me, but whatever works for you is good. Thanks.
