You should talk to a lithium battery professional. You are incorrect. The amps are drawn dependant on voltage supplied, no two batteries in series ever draw equally unless the voltages are absolutely equal (like two lithium) otherwise the battery with the lowest voltage will have more amps drawn from it than the others. Its just typically they are so close when talking two lead acids that it wont be noticeable. But one battery at 13.3-13.1v and the other 12.4-10.9v is a huge difference and you will roast that lead acid battery.
Thats just how it works. Thats why you cant mix lead acid with AGM as well, same thing will happen.
You could definitely do it in an emergency situation, but be careful not to draw the LA too far down.
You can draw a lithium down as far as you want, so your comment of "drawing either one down too far will damage them" is completely incorrect. Ive had my Ionics draw down to 0% and too low for the BMS to even turn on when i accidentally left my trolling motor plugged in and on over winter. I jumped them using an old school charger to wake up the BMS and they both charged to 100% and say 100% healthy in all cells in the app.
Sent from my SM-A516U using
Crappie.com mobile app