Small-battery maintainer
Battery Tender Junior Lead-Acid / Lithium Selectable 12V Maintainer
A low-amp 12 V maintainer with a selector for lead-acid (flooded, AGM, gel, sealed) or four-cell LiFePO4 batteries from 3 to 30 Ah. It suits small starting batteries rather than car batteries.
We earn a commission if you buy through links on this page, at no extra cost to you. It does not change what we recommend — see our affiliate disclosure. As an Amazon Associate I earn from qualifying purchases.
Best for
Small 12 V starting batteries, such as a generator's, that sit between uses
Specifications
| Output | 12 V; 1 A per Battery Tender's current product page (some listings for this SKU say 800 mA) |
|---|---|
| Battery types | Six-cell lead-acid/AGM (flooded, AGM, GEL, sealed maintenance-free) or four-cell LiFePO4, selected by button |
| Capacity | 3 Ah to 30 Ah at 12 V |
| Dead batteries | Won't start below 3 V; LiFePO4 recovery mode for 4–8 V batteries (3-hour limit) |
| Protection | Spark-free clips, reverse polarity, short-circuit |
| Input | 120 V AC |
| Certification | ETL / cETL |
| Warranty | 5-year limited |
Specifications as published by Battery Tender. Confirm against the current spec sheet before buying — manufacturers revise models without renaming them.
What's good
- Separate charge profiles for lead-acid and LiFePO4, so a lithium battery isn't left on a lead-acid float voltage
- Includes ring terminals, so it can stay wired to a battery that only gets used in an outage
- 5-year warranty, longer than either jump pack here
What's not
- Rated for 3–30 Ah only, which is too small for most car batteries. Check the battery's Ah rating before you buy
- The lithium mode covers four-cell LiFePO4 only, not every lithium-ion low-voltage battery
- Won't start on a battery below 3 V, so a fully flat lead-acid battery needs a different charger
Our verdict
This is a small-battery tool. It makes sense for an electric-start generator that sits between outages, as long as the generator manual confirms the starting battery's chemistry and its Ah rating falls inside the 3–30 Ah range. Pick the matching chemistry before connecting, and leave it on. For a car's 12 V battery, the GENIUS5 is the better fit.
Compare with the alternatives
- NOCO GENIUS5 — keeping a car-sized 12 v battery charged during storage, whatever its chemistry
- NOCO Boost Plus GB40 — waking a car with a flat 12 v lead-acid or agm battery without a second vehicle
- Battery Tender Jump N Start 1500 Amp Lithium Jump Starter (030-2020-WH) — a jump pack whose maker lists lithium 12 v batteries as compatible