Lithium Solar Battery

Lithium solar batteries are the most common battery in consumer electronics. They are used in everything from cellphones to power tools to electric cars and more. However, they have well defined characteristics that cause them to wear out, and understanding these characteristics can help you to double the life of your batteries — or more. This is especially useful for products that do not have replaceable batteries.
Battery wear is loss of capacity and/or increased internal resistance. The latter is not a well-known concept, but over time the battery is able to put out less amperage as the battery ages, and eventually the battery is unable to generate power quickly enough to operate the appliance at all even though the battery is not empty.
Time
Try to buy batteries when you need them, because lithium ion ages from the moment it leaves the assembly line. However, by following the recommendations below you can get a longer lifetime from the batteries you own. If possible, look for the date stamp on any battery powered item you intend to buy and try get the newest one. Often you will find it on there, either on the outside of the package or on the item itself.

Charging cycles
One cycle is fully charging the battery and then fully draining it. Lithium solar batteries are often rated to last from 300-15,000 full cycles. However, often you don't know which brand/model of battery is in the item you buy.
Partial cycles will give you many more cycles before the battery wears out, so when possible do partial discharges and then recharge. Don't intentionally drain a battery before recharging for lithium solar batteries.
For some equipment this is not realistic, in electric lawnmowers and other outdoor tools for example, but the manufacturer will hopefully have selected a battery chemistry designed for this use case.

Storage/operating temperature
Try to keep your batteries cool whenever possible. Don't store a cellphone or other portable lithium battery in a car on a hot day, and keep them cool when not in use (bring your portable tool batteries inside instead of leaving them in an unconditioned shed/garage). Park an electric vehicle in the shade or a reasonable temperature garage when possible. Many EVs have active cooling of batteries so that will take care of this for you, although you still save battery power by parking in the shade or a conditioned garage.
Also, your pocket is about 30ºC, so store your cellphone on a desk and out of direct sunlight if you're in the office or at home when practical.

Charging characteristics
Charge your battery at a slow rate when possible. Avoid quick charging except for rare instances when you absolutely need the most juice as quickly as possible. Charging at 1/2 its capacity per hour is acceptable but chargers that can charge a phone in under 1.5 hours from empty can be very hard on the battery.
For power tools, try to get a slow charger instead of the quick chargers many of them come with. This is not always possible, but often is.

Discharging characteristics
Try not to abuse your battery by pulling as much power as quickly from it as possible. For an EV, flooring the acceleration pedal on a regular basis is not good for the battery. Similarly, power hungry games can drain cellphone batteries quite quickly as well. If your phone gets hot from high power use (and not the sun or high room temperature), it is an indication that you are punishing the battery.
Sometimes taking it easy on batteries is not always possible because some products, such as lithium-ion powered tools, are hard on the battery by design (drills, lawnmower, snowblowers, etc.). In these cases, manufacturers will typically use batteries designed for high drain rates (but have lower capacity), but anything you can do to be gentle on even these batteries will pay dividends in longer life. For power banks, try to use the power at a moderate rate.
Also you can "hack" this issue by buying and using a larger capacity battery if your device can handle it. For the same power draw, a larger capacity battery will have a lower percent drain per hour. This also reduces cycle count.
For items you don't use daily, check on your batteries from time to time in case they are draining themselves when not in use. For EVs and cellphones, this is not a noticeable problem, but for power tools and power banks it is a good idea to check on the battery every few months (or weeks if it drains itself quickly) and top it up to 50%-ish for storage.

Depth of charge
Unlike most other battery types (especially lead acid), lithium solar batteries do not like being stored at high charge levels. Charging and then storing them above 80% hastens capacity loss. So charge the battery to 80% or a bit less if that will get you through the day/week.
Similarly, for your EV if you have a long driving day planned, setting the software to charge to full by morning (not storing the vehicle overnight at full) and driving until you are below 80% rather quickly will not cause much extra wear to your batteries. In general, it's the storage time above 75-80% that causes most of the extra high charge wear.For storing batteries long term, charge them to about 50% and check on them every now and then.

Depth of discharge
According to many sources, lithium-ion doesn't like being fully discharged. So try to avoid draining your batteries below about 25% when possible. If unavoidable, then charge it back up to above 25% as soon as possible so the time spent near empty is minimized.