DIY Battery Projects: Picking a Sealed Battery
Updated: Oct 22
Small sealed lead-acid (SLA) batteries power DIY alarms, lights, small power banks and hobby builds. This guide explains how to choose one and use it safely, based on Power-Sonic's Sealed Lead-Acid Batteries Technical Manual. Always check the datasheet and instructions for the exact battery you buy.
Why a sealed lead-acid battery
Power-Sonic describes its SLA batteries this way (Power-Sonic SLA Technical Manual, p. 1):
No topping up. There is no need to add electrolyte, because gases generated during charging are recombined inside the battery.
Flexible mounting. They can run in virtually any orientation without loss of capacity or electrolyte leakage, but upside-down operation is not recommended.
Pressure relief. Low-pressure one-way relief valves release excess gas and then reseal.
Cyclic or standby. The same battery may be used in cyclic or standby applications.
Step 1: Pick the voltage
Power-Sonic explains that lead-acid batteries are strings of 2 V cells connected in series, commonly 2, 3, 4 or 6 cells per battery (Power-Sonic SLA Technical Manual, p. 17). Batteries of the same model can be used in series and/or parallel to get the voltage and capacity you need (Power-Sonic SLA Technical Manual, p. 1). Don't mix batteries of different capacities, ages or makes (Power-Sonic SLA Technical Manual, p. 20).
Step 2: Pick the capacity (Ah)
How capacity is rated. Power-Sonic rates its PS, PSH and PSG batteries by a 20-hour constant-current discharge at 20 °C (68 °F) to 1.75 V per cell. Its example: a 1.1 Ah battery delivers 55 mA for 20 hours (Power-Sonic SLA Technical Manual, p. 6).
Rate matters. Capacity increases when the discharge current is lower than the 20-hour rate and decreases when it is higher. Power-Sonic's tables show the capacity at 10-, 5- and 1-hour rates (Power-Sonic SLA Technical Manual, pp. 5–6).
Temperature matters. Rated capacity is 100% at 20 °C (68 °F). It rises slowly above that and falls as temperature drops. At any temperature, a higher discharge rate means less available capacity (Power-Sonic SLA Technical Manual, p. 9).
Allow a break-in. Power-Sonic says full capacity is reached only after a few cycles or some time on float charge (Power-Sonic SLA Technical Manual, p. 6).
Step 3: Pick the right charger
Power-Sonic gives different charging rules for two kinds of use (Power-Sonic SLA Technical Manual, p. 16):
Cycle use: the initial charge current must not exceed 0.30 × C amps. Charge at 2.45 ± 0.05 V per cell. When the current the battery accepts falls below 0.01 × C, the battery is fully charged, and the charger should be disconnected or switched to a float voltage of 2.25 to 2.30 V per cell.
Standby use: use a constant float voltage of 2.25 to 2.30 V per cell, again without exceeding an initial charge current of 0.30 × C.
Power-Sonic calls continuous over- or undercharging "the single worst enemy of a lead-acid battery". It says to make sure the charger is disconnected after cycle charging, or that the float voltage is set correctly (Power-Sonic SLA Technical Manual, p. 21). It also says temperature effects should definitely be considered when choosing a charging system, and that temperature compensation is desirable, especially outside 5 °C to 35 °C (41 °F to 95 °F). The manual includes a table of charge voltages by ambient temperature (Power-Sonic SLA Technical Manual, p. 18).
Step 4: Protect against over-discharge
Power-Sonic recommends disconnecting the battery from the load when the end voltage is reached. That voltage depends on the discharge rate. Discharging below it, or leaving the battery connected to a load, impairs the battery's ability to accept a charge. Power-Sonic suggests voltage cut-off circuits to prevent this (Power-Sonic SLA Technical Manual, p. 12). Recharge as soon as possible after each use, and don't store the battery discharged (Power-Sonic SLA Technical Manual, p. 10).
Step 5: Mount it and enclose it safely
From Power-Sonic's do's and don'ts (Power-Sonic SLA Technical Manual, pp. 20–21):
Never use an airtight enclosure. Never charge or discharge a battery in an airtight enclosure. Gases from extreme overcharging or a short could vent and explode if ignited by a spark. Power-Sonic says the ventilation in most enclosures is generally enough.
Secure it. Fasten the battery tightly, add shock absorption if it will see shock or vibration, and mount it at the lowest practicable point in the equipment.
Keep it cool. Keep batteries away from heat-emitting components. If they must be close, provide ventilation. Power-Sonic says service life is shortened considerably above 30 °C (86 °F).
Space multiple batteries. Leave at least 0.4 in (10 mm) between batteries.
Keep sparks away, and don't charge it upside down. Don't place batteries near objects that can produce sparks or flames, and don't charge in an inverted position.
Be careful with the terminals. Don't apply heat or undue force to the terminals. If soldering is unavoidable, Power-Sonic says it must take no more than 3 seconds, with an iron of no more than 100 watts.
Protect yourself. Wear insulated gloves when handling batteries, especially when connecting series and parallel groups.
Power-Sonic gives operating limits of -40 °C to 60 °C (-40 °F to 140 °F) for discharge and -20 °C to 50 °C (-4 °F to 122 °F) for charging (Power-Sonic SLA Technical Manual, p. 9). For more on gas, see Hydrogen Ventilation for VRLA and UPS Batteries.
Step 6: Store it right
Recharge regularly. Power-Sonic says self-discharge is about 3% per month at 20 °C (68 °F) and rises at higher temperatures. Batteries should be stored at 20 °C or lower when possible and recharged every six months when not in use. Charge within 6 months of storage, or permanent capacity loss from sulfation can occur (Power-Sonic SLA Technical Manual, p. 10).
Disconnect for long storage. Disconnect batteries from equipment stored for a long time, to avoid drain and damage (Power-Sonic SLA Technical Manual, p. 20).
Disposal
Power-Sonic says not to disassemble batteries or throw them into a fire, where they may rupture or explode. Disassembled batteries are hazardous waste (Power-Sonic SLA Technical Manual, p. 20).
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Sources (checked 2026-10-21)
Power-Sonic, Sealed Lead-Acid Batteries Technical Manual: https://cdn.power-sonic.com/documents/SLA_Technical_Manual.pdf
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