Can Lithium Batteries Survive a 4WD Engine Bay?

The question is, can a lithium battery survive in the engine bay of a 4WD? Can it stand up to the punishment dealt its way with engine bay heat and icy cold desert mornings? Does it have enough power to run the winch? Will the alternator put out enough power to charge the battery? These are valid questions, so let's look and see what we can find out. 

It's Getting Hot In Here

The temperatures inside an engine bay can get hot on average sitting between 50 – 60C and even higher on a hot day where you can expect it to climb above 70C. The other thing to consider is that there are two kinds of heat within the engine bay, radiated and conducted, with conducted being well above radiated heat temperatures. 

For example, an exhaust manifold can reach temperatures of 600+ degrees on the surface, but the radiated temperature is a lot less than that so if anything touches the exhaust manifold, the heat conducted would melt it but if the item is a metre away from it, it won't melt but will gradually lose its properties over time. Think about all the cable ties under the bonnet. They don’t melt but over time they do degenerate and eventually break. 

Think about where the starter battery is mounted in the engine bay, it is as far away as the hottest parts, exhaust manifold and turbo, as possible. When the vehicle moves, the battery also gets hit with fresh air through the bonnet vent. If you install an auxiliary battery on the other side of the engine bay, the hotter side, it doesn’t seem to last as long as the starter battery. 

Before replacing the starter battery with a lithium battery, it would be wise to check the specifications about the operating temperatures, using the iTechworld 1420CA, the DCS 90Ah Hybrid and the Invicta 100Ah Hybrid Starter batteries as examples:

Looking at the figures, these batteries are suited to operating in most high-temperature conditions and offer high Lithium Cranking Amps that will easily start any engine. It is important to note that DCS and Invicta batteries have M8 connectors instead of post terminals so changes to the existing 12V cabling may be necessary.  

Will my winch operate?

The amperage that a winch draws will depend on the amount of load placed on it and how long it is in use. With no load (just spooling in and out) a typical 9,000-pound winch will draw 60-70 amps. It will draw about 250 amps under a 4,000-pound pull, and nearly 480 amps at 9,000 pounds. This is a big drain on any type of battery and one reason why it is highly recommended that the engine is kept running during winching procedures. 

A lithium battery delivers steady power for a long period whereas a wet-cell battery delivers peak power over a short period and a lithium battery charges at a much faster rate than a wet-cell battery. This means you can run a winch for longer before draining a lithium battery, however, Warn “strongly recommend that lithium batteries are not used for winching unless installed by a qualified installer.” The reason being “lithium batteries require additional circuit protection devices to protect the winch and battery.”

Are you strong enough?

A DCDC charger isn’t required to charge lithium batteries when used as a starter/dual battery setup, they are best connected directly to the vehicle alternator. 

Older alternators start outputting 14.2 volts but then drop to 13.6 –13.8 volts for the remainder of the time the engine is running.  This could be too low a voltage to fully charge a lithium battery as most have a nominal charge voltage between 14.0 and 14.6 volts. If this is the case with your 4WD, you may need to install an alternator voltage booster diode to ensure the lithium battery receives a charge. 

Another option is to replace the alternator with one that produces an output above 14.0 volts and so can recharge the lithium battery to 100% however this is an additional cost and could reduce the lifespan of the battery. A smart alternator is perfectly suited to a lithium starter battery as it automatically reduces the charge to the battery once it reaches 100%. 

Conclusion

Are lithium batteries suitable for installation in the engine bay? If you do the research and find the batteries that say they are designed to withstand the heat of an engine bay, then yes, but doing the installation correctly is the key. Heed the manufacturer's warnings, and if you have a winch, investigate what protection you need to include and if in doubt, get a professional to do the installation for you. It’s still too soon to see if the heat is detrimental to a lithium battery's life but if you think about how hot it gets in the cabin or canopy of a 4WD, you might be surprised that it is similar to your engine bay. 

Next steps

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