I'm thinking of putting 20 of these on my hood to keep my van battery topped off. Can anyone recommend a diode or charge controller for this?

These aren't as flexible as they advertise them as being and actually snap very easily. You might be better off buying a pre-built panel if you're trying to mount on your car.

I built a 20 cell panel and get 13.2v in bright sun with almost 6a of output, but if i connect straight to a sla 12v, will these leak at night?

It's always better to use a charge controller between solar panels and a charger. Even during the day when you have a cloud or some shadow pass by, your volts can drop and battery current go back into the cells. Without a charge controller, you can use a diode to make sure current only flows in one direction. Search for solar diodes you'll find something cheap that'll do the trick for you.

Best Sellers Rank	#709,334 in Patio, Lawn & Garden ( See Top 100 in Patio, Lawn & Garden ) #2,617 in Solar Panels
Brand	Sunpower
Efficiency	High Efficiency
Material	Monocrystalline Silicon
Maximum Power	3.6 Watts
Maximum Voltage	0.6 Volts
UPC	672299506695

Flexible Solar Cells E60 C60 5x5 3.6W Monocrystalline Cells for DIY Panels (100, No Busbars)

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