Every battery charger gets a score from 0 to 100% built from four factors, which maps onto the 5-point rating shown on the site (a 0% score would be 1.5 stars; a perfect score, 5). Each factor is scored against fixed reference points, not against the other products in the list, so adding a new model never moves another model’s rating. Chargers are grouped by charge current, maintainers up to 5 A and chargers over 5 A, and value and current have their own scale for each group.
| Factor | Measures | Weight |
|---|---|---|
| Value | price per amp of charge current | 35% |
| Charge current | maximum charge current at 12 V | 20% |
| Features | lithium mode, temperature compensation, repair mode, power supply mode | 25% |
| Warranty | warranty length | 20% |
Where the numbers come from
Charge current, voltages, charge modes and warranty come from the maker’s product page, spec sheet or manual, or the maker’s own copy on its Amazon listing. Prices are checked at Amazon and the maker’s own store, and the lowest is used.
The factors
Value is the current price divided by the maximum charge current at 12 V, on a log scale, so going from $20 to $10 per amp counts as much as going from $10 to $5. For maintainers, $60 per amp scores zero and $8 full marks; for chargers over 5 A, $30 per amp scores zero and $4 full marks.
Charge current is the maximum charge current at 12 V: for maintainers, 1 A scores zero and 5 A full marks; for chargers, 8 A scores zero and 25 A full marks.
Features counts four things that widen what a charger can safely charge: a lithium (LiFePO4) mode, temperature compensation, a repair or desulfation mode, and a power supply mode that holds a vehicle’s settings during a battery swap. Each is a quarter of the factor.
Warranty is the length of the warranty: 1 year scores zero and 5 years full marks.
What isn’t scored
Voltages, a separate AGM mode, engine start current, the largest battery it’s rated for, ingress rating and weight are listed but not scored.
Missing data
If a figure isn’t published, that factor gets the neutral middle score (50) and the product page marks it as estimated.
Ties and discontinued models
Products are ranked by score within each group. Discontinued models stay listed but rank below every current model and can be hidden with the “Hide discontinued” filter.