When evaluating one battery brand against another, always compare the physical size and weight of the batteries (average 40WH/kg) and carefully compare the manufacturers specification data sheets. Make sure they are constructed using the same technology (e.g. AGM, GEL).
Battery C Rating
In addition to the stated voltage and Ah capacity, SLA batteries have a "C" rating designed to meet specific load applications such as C5, C10 and C20. The vast majority of SLA batteries are rated C20 which means they are designed to provide 1/20th of the stated Ah capacity for 20 hours to 10.5V. For example, 7Ah/C20 = 350mA load for 20 hours.
When comparing like-for-like batteries, make sure that the stated Ampere hour (Ah) capacity is specified at C20 (20hr rate). This important "C" rating is often missing on the battery. For example, if brand "A" is specified at 7Ah and rated at C20 (20hrs) and brand "B" is specified at 7.2Ah but rated at C15(15hrs), brand "A" will out perform brand "B" by 5hrs. If both batteries show the Ah rating but not the "C" rating, you would incorrectly assume brand "B" would out perform brand "A".
When evaluating new out-of-the-box batteries, always allow them to acclimatize to 20 - 25°C (65 - 77°F) before testing, as the stated Ah can only be verified at this temperature. Also take into account that new batteries may not come fully charged and normally self-discharge at 3% per month whilst in storage.
ACT Intelligent Battery Testers
The GOLD-PLUS is programmed to perform a C20 test in seconds and displays the Ah capacity at the 20hr rate. Based on this, the GOLD-PLUS would correctly display 7Ah for brand "A" and 6.5Ah for brand "B". This enables you to compare both batteries Ah capacity at 20hrs, irrespective of the stated Ah capacity and without knowing the batteries "C" rating.
To obtain accurate, repeatable Ah readings, connect the GOLDPLUS clips TIGHTLY TO THE BATTERY TERMINALS ONLY and not to high resistance steel bolts screwed into the battery posts. When testing batteries with recessed posts, use the ACT 3532 Battery Terminal Connectors.