I owned Toyota Prius. When the battery was dying, the battery's SoC was low when it
was turned on in the morning, even if it was close to full the night before when it was parked. After about a week off this, it became unstable. Gas engine would run and the battery would charge to full quickly, then the gas engine would cut off and the battery would be low quickly. Then the dreaded red exclamation triangle came on. Without the main traction battery, car is pretty much useless.
Let's assume the battery lasts 10 years, 120K miles. I got 12 years, 150K miles from my Prius, but let's take a conservative estimate. Let's further assume hybrid battery costs 1/2 that of pure EV battery cost, because the capacity is lower. Considering Nissan Leaf battery is $5500 and Prius battery costs $2300, that's pretty close estimate. Labor for battery replacement on Prius adds $1200, so the total is about $3500; let's assume labor for Leaf is the same.
Suppose one has gas engine only car. One has to maintain the car through oil changes and so on. There may be repairs to be made, such as changing the water pump. But all the maintenance and repairs are for gas engine only. If one assumes hybrid / EV replaces the battery after it's worn out, and assuming it will last another 10 years, 120K miles, maintenance cost for equivalent gas car should be for 20 years, 240K miles.
5K service at $50 : 240K/5K * $50 = $2400
15K service at $250: 240K/15K * ($250 - $50) = $3200
30K service at $450: 240K/30K * ($450 - $250)= $1600
Actually, gas car's maintenance is even lower, because one wouldn't take 10 year old car with 120K miles to the dealer for 5K service. But they also tend to break down, such as water pump, which adds repair cost. It's hard to say how high that will be (probably lot higher). But for the sake of argument, let's assume dealer maintained throughout and no repairs are needed.
Suppose one has pure EV. There's not much maintenance to speak of until the battery capacity is down so much or erratic that it needs replacement. About the only major service is coolant replacement, which should be less in cost than 15K ICE maintenance cost of $250. But let's assume 30K service price of $450 as conservative estimate.
EV Maintenance cost : $450
Battery + labor : $5500 + $1200 = $6700
Total : $7150
But if one owns hybrid, one has to perform all the regular maintenance of the ICE, and one has to worry about dead battery.
Hybrid's ICE maintenance : $7200
Hybrid's battery + labor : $2300 + $1200 = $3500
Total : $10700
It's not looking good for Hybrid compared to gas car. There's no way hybrid can make up the initial acquisition price difference from gas car and make up the maintenance cost difference from energy savings.
Hybrid doesn't compare well to pure EV. Energy cost is higher due to using gas engine. Even if one doesn't use gas in hybrid as in driving short distances with plug-in hybrid like Volt, heavier weight eats energy. Hybrid also has to deal with all gas car issues, such as oil change and so on, wasting time at the dealer.
Unfortunately, most pure EV tend to cost more than Hybrids. This is where SparkEV shines; it costs less than all hybrids on the market! It also has higher performance than hybrids costing two or three times as much! Buying hybrids doesn't make much sense when SparkEV is available, not even the plug-in hybrids. In fact, plug-in may be worse due to larger battery costing even more when it comes to replacement.