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101 Renewable - Interstate Deep Cycle Charging Recommendation

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Last Updated
10th of January, 2020

(111 votes)
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Intertate Deep-Cycle Batteries Charging Recommendations

Note: this article is limited is scope to Interstate deep cycle batteries used in solar industry,

Charging Recommendation for all Deep Cycle Batteries whose part number start with the letter "U" :

This includes the following battery part numbers:  U1800, U2000; U2200, U2300, U2400, U2500, U3050, U3050HC, UL-16, UL-16HC, U1450, U1850, U1850HC; U8VGC, U8VGCHC, USRM8V19, USRM8V-21, USRM8V-24, USRM8V-27; USRM8V-26, U-BIG-JOE; USRM-16TF, USRM-8D) 

Voltage of the battery system  Charging Current
Bulk Charge Voltage
Absorption Voltage
Absorption Time in Hours
Float Voltage

Equalization Voltage Equalization Time in hours
6 C / 10 7.2 7.75 2 to 4 6.6 7.8 2

C / 10 9.6 10.33 2 to 4 8.8 10.4 2

C / 10 14.4 15.5 2 to 4 13.2 15.6 2

C / 10 28.4 31 2 to 4 26.4 31.2 2


Need to determine the volts and amp-hours for your battery? See below
  1. C = 20 hour capacity in Amp-hours,
  2. Float condition is for long term storage (several weeks),
  3. Equalize every 4 to 8 weeks and always after a normal charge,
  4. Be sure to leave the vent caps on your battery (or batteries) while charging them. 

Charging recommendations for UAGM8D (rated at 250 AH at the 20-hour rate): 

Battery Voltage 
Charging Current
Bulk Charge Voltage
Absorption Voltage
Absorption Time in Hours
Float Voltage

Equalization Voltage
Equalization Time in hours
12 C / 10 14.4 14.4 2 to 4 13.2 14.4 2


1. C = 20 hour capacity in Amp-hours,
2. Float condition is for long term storage (several weeks).
3. Equalize every 4 to 8 weeks and always after a normal charge

Charging recommendations for 6-volt deep cycle batteries. GC2-XHD, GC2-HD, GC2-RD:

Nominal Battery
Charging Current

Bulk Charge
Voltage (2.41 VPC)
Absorption Voltage
(2.55 VPC)
Absorption Time
in Hours

Float Voltage
(2.23 VPC)

Equalization Voltage
(2.6 VPC)
Equalization Time
in Hours

6 Volt
(3 cells)
C / 10 7.23 7.65 2 to 4 6.7 7.8 2
8 Volt
(4 cells)
C / 10 9.64 10.2 2 to 4 8.92 10.4 2
12 Volt
(6 cells)
C / 10 14.46 15.3 2 to 4 13.4 15.6 2
24 Volt
(12 cells)
C / 10 28.92 30.6 2 to 4 26.8 31.2 2
36 Volts
(18 cells)
C / 10 43.38 45.9 2 to 4 40.2 46.8 2
48 Volts
(24 cells)
C / 10 57.84 61.2 2 to 4 53.5 62.4 2


Other Charging Notes/Tips/ Definitions:

Temperature Compensation: Increase voltage by .028 volts per cell for every 10 degrees below 80 F. Decrease voltage by .028 volts per cell for every 10 degrees above 80F.

Typical phases on multi-stage chargers:

Bulk: Initial phase where the voltage builds and the most current is provided to the battery. This is typically where the maximum current that the charger is capable of providing is supplied to the battery. i.e. A 10 amp charger will provide at or near 10 amps during this phase.

Absorption: The phase where the voltage set point is held constant. Current will decrease gradually during this point as the battery internal resistance comes up.

Float: The maintenance or finishing phase of the charging cycle. Voltage is set at a minimum during this phase (usually 13.0c-13.5v) and current drops significantly. The battery should be nearly complete by the time this phase is reached.

An anti sulfation stage may be added where voltage spikes to high levels for very brief time periods for a set amount of time determined by the charger manufacturer, to convert the battery active material back to it's original state. Badly sulfated batteries will not usually respond to this charging regime and will need to be replaced.

Visitor Comments
  1. Comment #1 (Posted by JOHN OSTLUND )
  2. Comment #2 (Posted by SolarBrands )
    It is important to use the battery manufacturer's charging recommendations whenever possible for optimum performance and lifespan. This are Deep Cycle Batteries and they do discharge up to 20% from their nominal capacity. But as thumb rule we have to work above this limit and help the battery to regenerate the plates capacity before permanent chemical destruction may occur. In the same time repeated fast charges on a battery may overcharge a battery and reduce the service life. The best way it is to slow recharge a battery using the RC factor for that specific battery. At the beginning you will perform a bulk charge. You will leave the battery under a float charge to finish the bulk charge and to compensate the natural capacity discharge in time through internal native resistance of the battery and you will perform an equalization charge every 8 weeks considering some of the cells are more exposed as others all of that after a full cycle charge has been performed. RC factor is the reserve capacity factor for your battery and you must multiply that one to 0.6 to find real value for the time you have to charge that battery, to reach the reserve capacity. Your system has to restart the bulk charging of your battery when the voltage on the battery is shy over 7.23V and has to slow charge as long as RCx0.6 in your case is 415 min @ 25A charging current for quality charging. In case of a fast charge the manufacturer recommends 110 min @75A. I hope that will help you check your system and set up the charge controller.
  3. Comment #3 (Posted by Phil )
    My question is what are the charging specs. Interstate GC12 batteries? These are 12 volt golf cart batteries. I have 4 in series to equal 48 volts. Thanks
  4. Comment #4 (Posted by William )
    I have a marine battery 12V, 27DC, 105AH, Interstate which are the charge values ​​of that battery.
  5. Comment #5 (Posted by John Stagg )
    In my camper, I have an Interstate, 12 volt battery, Model # SRM24. Can you provide the discharge rate at the following Amps - 25,15, 8?
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