To prevent the permanent loss of gases so that the recombination process has time to take place, each cell can hold approx. 1.6 pounds per square inch (psi) of pressure without venting. (the battery has a VALVE-REGULATED lead-acid design).
Large batteries with very large cells will bulge somewhat as this normal pressure builds. This is especially true in higher temperatures because the polypropylene case is pliable. Therefore, a certain amount of bulge is normal. The valves only let the gas out, never in.
A partial vacuum (sucked-in appearance) can form within a sealed battery under various circumstances.
Battery temperature and ambient pressure play a role, but predominantly the recombination and discharge reactions are responsible. After charging ends, the recombination reaction continues until most oxygen in the battery is consumed. The total volume within the battery decreases slightly during a discharge. Deeply discharged batteries often have a “sucked-in” appearance. Batteries with large cells may display this appearance even when fully charged. If a battery bulges severely on a charge, it may indicate a blocked valve or an overcharged situation. When a battery is in this situation, it should be removed from service.
Discover VRLA (Valve Regulated Lead-Acid) DRY CELL AGM and GEL batteries work on a recombination principle.
Oxygen gas is produced at the positive plates during charge. The charged negative plates react first with this oxygen and subsequently with the electrolyte. Water is produced, and the negative plates are slightly discharged. Additional charging recharges the negative plates instead of producing hydrogen gas. Since very little hydrogen and oxygen are lost and the water (H20) is retained, we say that the gases have recombined.
To work correctly, the oxygen produced must be retained in the battery until the reaction is completed. The positive pressure allows the gas to be retained. If any VRLA DRY CELL AGM or GEL battery is overcharged, gas will be vented from the valves and Hydrogen as well as oxygen will be released. If continued, the electrolyte will eventually dry out, and the battery will fail prematurely. This is why charging limits are so critical. In a sealed battery, a balance must be maintained between the hydrogen, oxygen and recharge reactions that take place, which requires the process to be value-regulated. If a VRLA DRY CELL AGM or GEL battery is opened:
- The negative plates are exposed to extra oxygen from the atmosphere
- This excess oxygen upsets the balance
- The negative plates become discharged
- The positive plates may be subsequently severely overcharged
- The battery will fail prematurely
Installing batteries in marine applications (especially salt water) requires special attention.
The cables used should be marine-approved and should be tinned copper. If you use any other type of cable, be prepared to spray and coat the cable and connections with silicone or another type of grease, such as Vaseline. Use silicone-lined heat shrink tubing to cover terminal connections to protect against corrosion. The main concern is keeping the marine atmosphere away from exposed terminals or connections.
CAUTION/DANGER: Do not allow battery electrolytes to mix with salt water. Even small quantities of this combination will produce chlorine gas that can KILL you!
To convert Amp Hours (AHC20) to Reserve Capacity, divide the known C20 Ah rating by .54 (maximum) and .58 (minimum) to get a good average result. More ampere-hours (or RC) are better in every case when looking for a deep-cycle battery. This conversion method will allow you to convert and compare competitive data GENERALLY.
75Ah / ,54 = 138 minutes of reserve capacity at a 25A draw or 75Ah / ,58 = 129 minutes of reserve capacity at a 25A draw.
Therefore, a battery rated at 75AH C20 can be estimated to provide between 138 and 129 minutes of reserve capacity at a 25A draw.
To convert BCI Reserve Capacity at 25 Amps to equivalent Ampere-Hours at the 25 amp per hour rate, multiply RC by .4167. More ampere-hours (or RC) are better in every case when looking for a deep-cycle battery. This conversion method will allow you to convert and compare competitive data GENERALLY.
180RC x .4167 = 75Ah at the 25A rate.
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