The Raven uses those tiny lipos as a means of limiting the current which can be sourced through the FETs in a dead short. The Main/APO channels only have 9 amp FETs because normal ematches are unlikely to cause short during a deployment event. Motor igniting causing a dead short has "a high chance of happening" according to Featherweight, so the 3rd and 4th channel FETs are rated to 40 amps.
From Adrian A:
"A 300 mAhr 2S battery will definitely put out enough current to permanently damage a Raven's Apogee or Main output channels in the event of a short. Output shorts are fairly common during user ground testing, and they happen every time during airstarts with head-end ignition. Persistent shorts after a deployment charge ignition are less common, but possible as well. The Raven's Apogee and Main FETs can handle over 8 Amps for the 1-second firing duration, which is higher tolerance than some (most?) altimeter output channels, and 100s of times more power than is required to fire ematches. The Raven's 3rd and 4th channels, typically used for airstarts, use a larger FET that can handle over 25 Amps. They might stand a chance against the battery you're recommending in a short situation, but there are slightly larger lipo packs that can kill even them.
Please, Bob, help spread the word to avoid powering a Raven with a lipo battery that's larger than 1S, 170 mAhrs. This is spelled out in the user's manual, found here. I just patched up a Raven a couple of days ago that had its Apogee FET blown out, the traces underneath the FET melted, and also opened the current sense resistor. The user said he used a 300 mAhr battery like the one you're recommending. He had an LED connected to the output without a current-limiting resistor. I couldn't replace the MOSFET on the bad channel because of the trace damage. If it had flown again before being fixed, the dead current-limiting resistor would have prevented a deployment on any of the channels. In more mild cases, a FET that has an overcurrent failure will stay permanently shorted, which can allow output current to fire whatever is connected as soon as the switch is turned on.
With the Raven (and probably some other altimeters too) small lipo batteries work great with any ematch and just about any ignitor other than a Copperhead. Larger lipo batteries are unnecessary and dangerous for typical rocketry applications. Thanks for your help with this."
As I understand it this makes them a bit of an iffy combination with the wifi switch if you're doing airstarts. I've used them successfully together, without issue, but I did not do any motor ignition.
I assume the only reason we don't hear about this with other altimeters is because they are used less frequently for airstarts, or are physically larger so they have current limiting/bigger FETs/etc.
