Antigravity Group 51R Lithium Battery for Honda Civic

Antigravity Group 51R Lithium Battery - Part #AG-51R-30-RS

If you've got an EG, EK, DC2, DC5, or any gas Civic through 2021, the battery sitting on your shock tower is a Group 51R lead-acid pack that weighs about 30 lb. The Antigravity Group 51R RE-START is the 30 Ah lithium version of that same case: 11.25 lb, 1200 cranking amps, and a keyfob that jump-starts the car from the driver's seat if you ever leave the lights on.

What It Is and Why It Works

This is a LiFePO4 pack with a full battery management system built into the case, in the exact 9.4 x 5.2 x 8.6 inch Group 51R footprint with the positive post on the right. It drops into the factory tray, uses the factory hold-down, and the stock cables reach the M8x1.25 threaded terminals with no adapters. You're taking 18 to 20 lb off the front corner of the car, which on an EK or DC2 with a K-swap already up front is the cheapest real weight you'll ever remove.

The RE-START part is what separates it from the other lithium packs. The BMS watches voltage, and if you leave the dome light on overnight it shuts the pack down before it goes flat, holding back enough to crank the engine. You press the keyfob (two come in the box), or the button on the lid, and it wakes up and starts the car. No jumper cables, no hood. The same BMS handles overcharge, short circuit, thermal, and cell balancing, which is why Antigravity puts a 5-year warranty on it instead of the 1-year most race lithium carries.

Cranking is the other thing you'll notice. A stock 51R lead pack is rated somewhere around 500 CCA. This is 1200 cranking amps, so a high-compression K24 or a cold B18C turns over noticeably faster and the voltage doesn't sag at key-on.

Specs

Fitment

It does not fit the FK8 or FL5 Civic Type R, the DE5 Integra Type S, or any 2022-and-up Civic. Those cars moved to the H5 / Group 47 tray, and the Type R and Integra Type S take Antigravity's AG-H5-40-RS instead. Civic Hybrids (2006-2015, and the 2025-up) are not Group 51R either. If you're unsure, measure your tray and confirm the positive post is on the right when the terminals face you; a plain Group 51 has the posts reversed and the stock cables won't reach.

What to Know Before You Buy

Throw away your lead-acid tender. A standard tender or AGM charger runs a desulfation or float profile that pushes past 14.6 V, and that voids the warranty and can cook the BMS. If the car sits for more than a few weeks at a time, use a LiFePO4 charger like the Antigravity SC-4. A stock Honda alternator regulates around 14.3 to 14.5 V, so daily driving keeps it happy with no charger at all.

Register it with Antigravity within 30 days of purchase or you have no warranty. Keep both keyfobs; Antigravity won't replace them, and the RE-START button on the lid is your only backup if a fob walks off. The Bluetooth tracker that shows state of charge on your phone is sold separately and worth having on a car that sits.

This is the 30 Ah street battery. Antigravity makes a 24 Ah race-only version in the same case that's 3 lb lighter; it's meant for track cars with no stereo and no parasitic draw, and it's not this listing. If you're running a big amp, an aftermarket alarm, or anything that pulls current with the key off, the 30 Ah is the one you want. Parasitic drains that pull the pack below 10 V are excluded from warranty, so if you've got a mystery draw, chase it first.

Install is the same as any 51R: negative off first, positive off, lift the old pack, drop this one in, positive on, negative on, torque the terminals snug rather than gorilla-tight. If it's been sitting in a warehouse it may arrive asleep; press a fob and it wakes up.