How to Maintain Deep Cycle Batteries

Proper Care and Maintenance of Deep Cycle Batteries


New batteries should be given a full charge before use.
New batteries need to be cycled several times before reaching full capacity (20-50 cycles, depending on type).  Usage should be limited during this period.
Battery cables should be intact, and connectors kept tight at all times.  Systematic inspection is recommended.
Batteries should be kept clean, free of dirt and corrosion at all times.
Vent caps should be kept in place and snug during operation and battery charging.
Batteries should be watered AFTER charging UNLESS plates are exposed before charging.  If exposed, plates should be covered by approximately 1/8" of water.  Check water level after charging.  The water level should be kept 1/4" below the bottom of the fill tube in the cell cover.  (A Pro-Fill watering system can eliminate the guesswork of proper fill levels).
Water used to replenish batteries should be distilled or treated to not exceed 200TDS (Total Dissolved Solids...Parts Per Million).  Particular care should be taken to avoid metallic solids (iron).
Batteries should NEVER be discharged below 80% of capacity (approximately 1.8 volts per cell under normal load;  1.98 volts open circuit; 1.145 specific gravity).  Proper battery sizing will help avoid excessive discharge.
Battery charger should be sized to fully charge batteries in an eight hour period.  Charger should be kept in proper operating condition including fuctional controls, secured and sheilded cables, A.C. and D.C. plugs intact.
In situations where multiple batteries are connected in series, parallel or series/parallel, a replacement battery(s) should be of the same size, age, and usage level as the companion batteries.  DO NOT REPLACE JUST ONE BAD BATTERY!  Never put a new battery in service with a pack which has 50 or more cycles.  Either replace will all new batteries, or use a good used battery(s) with same cycle use.
Periodic battery testing is an important preventative maintenance procedure.  Hydrometer readings of each cell (fully charged) gives an indication of balance and true charge level.  Imbalance could mean that need for equalizing and is often a sign of improper charging or a bad cell.  Voltage checks (open circuit, charged and discharged) can locate a bad or weak battery.  When checking specific gravity, it is possible to convert the reading to what the open circuit voltage should be.  The formulas is to add .84 to the hydrometer reading and multiply by the number of cells.  Thus, a fully charged battery with a reading of 1.265 SpGr will have an open circuit reading of 12.63 volts.  Load testing will pick out a weak or bad cell when other test methods fail.  The point is to look the abnormal.  A weak cell or battery will cause premature failure or erratic function of companion elements such as batteries, navigation systems and other electronics.
DO NOT use a mismatched charging source of any type.  An undersized charger will never get the job done, no matter how long it tries.  An over-sized charger may cause excess gassing and heat that could possibly result in thermal runaway, and ulitmately, and explosion.
As batteries age, their maintenancerequirements change.  Generally, their specific gravity is higher.  Gassing voltage goes up.  This means longer charging times and/or higher finish rates (higher amperage at the end of charge).  Usually, older batteries need to be watered more often or their capacity may decrease.
Inactivity can be harmful to Deep Cycle Batteries.  If they sit for several months, a "boost" charge should be given; more frequently in warm climate (about once a month) than in cold climates (every 2-3 months).