Quote Originally Posted by doggone View Post
First...get a digital multimeter. Most of even the budget models have very accurate DC voltage measurements. You can get one at Lowes or one of the auto parts stores. Generally steer away from the bargain bin ones....just a decent multi meter you can use all purpose.

Always double check them occasionally no matter what charger you have. As an all around rule of thumb...if you have around 12.7 volts you have a fully charged battery. 12.4 or so will act okay at first but you will notice you run out pretty fast,it's either a battery getting weak or ...your charger is shutting off before it's fully charged.Anything less.. considerably undercharged or bad cell or cells.

Put any battery you want to test on a charger first. When the charger shuts off...(if it doesn't your battery is probably definitely bad) and the see what voltage you have. You should have 12.7 or better...some chargers will leave a slight over charge of 13.1 volts or so. Put a small load on the battery for 20 minutes or so like a nav light. Then check to see if you have 12.7 or more...if you don't weak battery.

Generally speaking don't expect a lot from a 24 or even a 27 class battery. If you seriously need to power a troller and a multitude of devices...start with at least a 29 class or parallel smaller ones or multiple batteries for different loads . If you are going to stay on a budget with flooded cell batteries in the 100 dollar range...get the highest reserve capacity and best warranty you can. Wal-Mart batteries are not bad...it has a lot to do with treating them right. You will kill any of the low end batteries with incorrect maintenance . Three to five years tops out of them typically even when you treat them right.

centage of Charge 12 Volt Battery Voltage 24 Volt Battery Voltage Specific Gravity
100 12.70 25.40 1.265
95 12.64 25.25 1.257
90 12.58 25.16 1.249
85 12.52 25.04 1.241
80 12.46 24.92 1.233
75 12.40 24.80 1.225
70 12.36 24.72 1.218
65 12.32 24.64 1.211
60 12.28 24.56 1.204
55 12.24 24.48 1.197
50 12.20 24.40 1.190
45 12.16 24.32 1.183
40 12.12 24.24 1.176
35 12.08 24.16 1.169
30 12.04 24.08 1.162
25 12.00 24.00 1.155
20 11.98 23.96 1.148
15 11.96 23.92 1.141
10 11.94 23.88 1.134
5 11.92 23.84 1.127
Discharged 11.90 23.80 1.120
Monitoring and Maintenance
The battery voltage should be kept at or above a 50% state of charge for maximum battery life. Keep the battery's electrolyte level to the indicated level and never let the plates be exposed above the electrolyte. Use only distilled water - not tap water, when refilling the batteries. Water is the only element used by your battery. You should never have to add acid to your battery. Do not overfill or fill when the batteries are discharged. Over-watering dilutes the acid excessively and electrolyte will be expelled when charging.
Equalization
Equalization is the controlled overcharging of a fully charged battery. This overcharge mixes the electrolyte, evens the charge among varying battery cells and reduces permanent sulfation of the batt
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