Do Car Battery Blankets Work?
4 lessons in this series, 13 min in total
- Do Car Battery Blankets Work? 4 min read
- Battery Blanket vs Battery Maintainer: Which Do You Need? 3 min read
- Block Heater vs Battery Warmer: Which Helps a Cold Start More? 3 min read
- At What Temperature Should You Plug In a Block Heater? 3 min read
This lesson draws on the retailer etrailer’s Kat’s and Zerostart product pages and expert answers, Rick’s Free Auto Repair Advice and owner reports on the Tahoe Yukon Forum. How we research explains the method.
Heated wrap or plain insulation
Two different products are sold as “battery blankets.” A heated one has an electric element inside the wrap and a cord that plugs into a wall outlet. An insulated one is just a sleeve or cover with no power, and many are sold as heat shields for hot weather as much as cold.
Insulation only slows heat loss. After a long, cold night, an unheated battery has little warmth left to keep in, so for winter starts only the heated kind does much.
Etrailer’s Zerostart listing says the 80 W pad gives a 60-70°F (33-39°C) rise in the battery’s core temperature over the outside air. That is the seller’s own figure, not an independent test, but it shows how much warming these wraps aim for.
What a warm battery buys you
Cold cuts the power a battery can deliver, and why a weak battery shows up in cold weather has AAA’s numbers. Keeping the battery warm overnight claws some of that back at the moment you turn the key.
Rick’s Free Auto Repair Advice says a battery heating blanket works, but isn’t the most effective way to get the most power from a battery in the cold; it prefers a plug-in maintainer that keeps the battery full.
Owner reports on the Tahoe Yukon Forum are mostly positive. A member who worked at a coal mine in northern British Columbia said the battery blanket, which he ran with a block heater and synthetic oil, saved his truck many times. Another member, whose truck came with a factory battery warmer, said very cold weather is when battery problems show up, so having one doesn’t hurt.
Warmth does not replace charge. A flat battery also freezes far sooner than a full one (freeze points by charge level), so keep it charged too.
Pick the length for your battery
These wraps go around the battery’s sides, so length matters more than wattage. Measure around your battery or check its group size on the label.
| Wrap | Power | Length | Battery groups listed |
|---|---|---|---|
| Kat’s 22100X | 60 W | 28 in (71 cm) | 26, 26R, 70 |
| Kat’s 22200X | 80 W | 36 in (91 cm) | 24, 24F, 27, 27F, 74 |
| Zerostart 2800063 | 80 W | 36 in (91 cm) | 24, 25, 27, 31, 34, 35, 38, 74 and variants |
The battery groups above are the ones etrailer lists. An etrailer expert said a Kat’s wrap that covers only three sides still helps, though less. Another noted a warning printed on the Kat’s heater not to overlap it, so don’t pick one much longer than your battery’s girth. Etrailer’s Zerostart listing says the pad is not for lithium-ion, nickel-cadmium or ABS-case batteries.
Kat's 22100X Thermal Battery Wrap
A 60-watt heated vinyl wrap for smaller car batteries that plugs into a household outlet. Retailer etrailer lists it for groups 26, 26R and 70 and for use below freezing. Measure your battery first.
Key specs
- 60 watts, 28 in (71 cm) long
- Etrailer lists groups 26, 26R and 70
- For use below 32°F (0°C), per etrailer
Paid link
View on Amazon (opens in a new tab)Kat's 22200X Thermal Battery Wrap
An 80-watt heated vinyl wrap for common car and truck batteries that plugs into a household outlet. Etrailer's experts say it has no thermostat and should run only below freezing. Measure your battery first.
Key specs
- 80 watts, 36 in (91 cm) long
- Etrailer lists groups 24, 24F, 27, 27F and 74
- No thermostat: use below 32°F (0°C)
Paid link
View on Amazon (opens in a new tab)Zerostart 2800063 Battery Warmer Blanket
An 80-watt, 120 V battery blanket with Thinsulate insulation and a 30 in grounded cord. No thermostat. Not for lithium-ion or ABS-case batteries; check your battery group first.
Key specs
- 80 watts, 120 V, 36 in (91 cm) long
- Listed for groups 24, 25, 27, 31, 34, 35, 38, 74 and variants
- 30 in (76 cm) grounded cord, no thermostat
Paid link
View on Amazon (opens in a new tab)Using one without trouble
Etrailer’s experts say the Kat’s 80 W wrap and the Zerostart pads have no thermostat, so they heat whenever they are plugged in. For the Kat’s 80 W wrap, an expert cited the instructions: don’t use the heater when it is above 32°F (0°C) outside. Another answer, credited to Kat’s, says to start it 1-2 hours before you crank the engine, or run it overnight when it is below freezing.
- Timer: an etrailer expert suggests an outdoor plug-in timer, or a thermo-switch that turns on below 32°F (0°C), so it doesn’t run on mild days.
- Cord: the 120 V Zerostart has a 30 in (76 cm) grounded cord, so you’ll likely need an outdoor-rated extension cord.
- Unplug before driving: an etrailer expert says you can crank the engine with the Zerostart pad plugged in, but should unplug it before you drive off so you don’t damage the cord.
Not every owner is a fan. A Wisconsin member on the same forum said he has seen battery warmers overheat batteries, mostly on generators, though he thinks they are fine if plugged in only overnight.
What a blanket can’t fix
A blanket warms the battery you have. It won’t recharge a battery drained by short trips or weeks of parking, and it won’t revive one that is worn out. If your battery is three or more years old and slow to crank, read whether to charge or replace it first.
If the car sits for days between drives, a maintainer may help more; battery blanket vs battery maintainer sorts out which you need. If the engine itself is the hard part to turn over, a block heater does more than a battery warmer.
