I just received my (2) EarthX batteries and plan to install them on the engine side of the firewall. I read in another forum a concern someone had about 'operating temperature' of the EarthX batteries which is -30C to 60C”(-22F to 140F). The EarthX manual says to not expose the battery above 200F. Has anyone measured operating temperatures under the cowl during ground and flight operations? If under-cowl temps are higher than the temperature envelope for EarthX batteries then I may locate the batteries on the cabin side of the firewall OR go with my original plan (engine side) and direct some outside air over the batteries to keep them within the Mfr. operating temperatures.

Appreciate any thoughts on this subject.

Thanks! Dave

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I think you need to mention which engine you are using, and any respondents should, as well. Temps on the engine side of the firewall are going to vary wildly since different engines have different cooling schemes and different placement of radiant sources of heat such as mufflers.  Also, the battery location and method of mounting will be a factor as to whether a box or clamping-band and shelf is used and whether or not there are air gaps or insulation between the battery and the box, clamping band, etc.

Seems I recall some Rotax owners attributed premature bungee wear due to radiant heat and even devised heat shields to protect the bungee ... but, of course, that's a mid-line structure in the firewall and temps could be quite different just a foot or so lateral to this where a lot of batteries sit!

I have a Jabiru 3300 and it is ironic that although early Jab's had a reputation for being difficult to cool in the 750's high-drag, low-speed airframe (my engine is a later production version which took some progressive tweaks, but runs quite cool), the environment around the engine under the cowl has always seemed cool! Maybe all those tweaks, etc., have a really good airflow going in there! Anyway, it has never seemed "hot" in the sense that the inside of the cowl paint has no heat discoloration and nothing seems particularly warm if the cowl is popped immediately after a flight. The muffler on the Jab is down low, near the cowl outlet, so it is nowhere near my EarthX ETX36D which is on the right lateral firewall and just under the firewall "shelf."  FWIW I flew it through last summer without problems in Tennessee's moderate heat.

If one obtained some non-reversible temperature strips in the appropriate range and stick them on their battery, it would be an interesting report!



John, I have a Viking 110 hp liquid cooled engine. Viking's website indicate coolant temps should be between 201 and 240 F (Green). Muffler discharges vertically through the cowl on the pilot side and my preliminary battery location is opposite the muffler on the passenger side firewall. I am going to fabricate a battery box with air gaps regardless if I mount it on the engine side or cabin side of the firewall. BTW...I live in southern California.


David -

I saw your post on the mounting the lith. batteries in your 750 with a Viking engine and that you live in SoCal.  I'm building a 601 XL with a Viking engine and live in Orange County (Irvine). I've got the pretty much all the component parts done/built, engine running, instruments installed and just completing the canopy. I mounted dual Lith. batteries between the dash and firewall and it worked out great and very clean. If you would like to come by and see them I'd be glad to show you. Love to see your build if your interested.  Us Viking guys need to stick together!

Thanks - Brad Rawls - Brad@ocbis.com.

Hi Brad, I would love to see your bird...I will connect with you 'offline'.

Best, Dave

I am installing mine behind the firewall for temperature reasons. I will post some pictures once I finish.

I think it would depend a lot on the spot you put it on.  Mine is on the engine side compartment of the firewall, on the low side.  It's shielded by a decent box I made for it so it should be fine.  My exhaust is on the lower front of the engine.  If it does seem to warm in there, it would be easy enough to move it to the other side of the firewall, but I think it will be fine.  Still have to make a lid for it though...


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