What is the appropriate translation for 'energy'?

Question

There are many times when I want to tell someone that I don't have enough energy to do something. These are close but not exactly what I want:

我太累。 I'm not too tired, I just don't have as much energy as I used to do what I want to do (like play basketball for 8 hours straight).

我的能力不够。Here, it's not that I don't have the ability to… I can do that, I just don't have the energy to do that (like play basketball for 8 hours straight).

Other contexts where I would like to use this phrase:

• "I have other responsibilities, so I don't have the time or energy to sit beside you and manage you."
• "The players aren't lazy, they just don't have enough energy to keep up with the other team."

Answer 1

The translation of energy to Chinese is really a tricky one, or very "context sensitive". I will try to give example one by one.

1. 体力 Body(Physical) Power

   我太累。 I'm not too tired, I just don't have as much energy as I used to do what I want to do (like play basketball for 8 hours straight).

   [繁] 我太累, 體力不夠了,不復當年啊。
   [简] 我太累, 体力不够了,不复当年啊。
   
   Enerygy ->  体力   body(physical) strength / body energy
               不够了 no enough / run out
   
               不復   not as (good as)
               當年   years ago / in the past
   

   So 我的能力不够 should be 我的体力不够.

   The following example fall in the same usage

   The players aren't lazy, they just don't have enough energy to keep up with the other team.

2. 精神 Will Power / Brain Power

   I have other responsibilities, so I don't have the time or energy to sit beside you and manage you.

   [繁] 我有其他事情要處理, 沒有那麼多時間精神跟在你後面管著你。

   [简] 我有其他事情要处理, 没有那麼多时间精神跟在你后面管着你。

   事情要处理  things that have to be taken care of / responsibilities (责任)
   精神       energy / will power (mental state related)
   

3. PS

   体力 is always referring to physical/body strength/state. As 体 mean body.

   精神 can be referring to mental state only or both.

   [繁] 他今天精神很好
   He look good today.
   He is in good shape today.
   

   精力 can refer to both physical or mental state, or both at the same time. Mostly interchangeable with the above two.

   [简] 我太累, 体力 不够了,不复当年啊。

   [简] 我太累, 精力 不够了,不复当年啊。

   [简] 没有那麼多时间 精神 跟在你后面管着你

   [简] 没有那麼多时间 精力 跟在你后面管着你

Answer 2

In general, 精力 is the word for human energy as opposite to tiredness. 时间和精力 (time and energy) is indeed an idiom in Chinese.

"I have other responsibilities, so I don't have the time or energy to sit beside you and manage you."

我还有别的事，没有时间和精力坐在你旁边伺候你。

When referring to sport stamina, 体力 is more accurate.

"The players aren't lazy, they just don't have enough energy to keep up with the other team."

队员们不是懒惰，而是体力不如对方。

When referring to vigorous personality or lifestyle, the general word is 活力. Some certain phrases containing 精力 like 精力充沛/精力旺盛 has similar meaning, but not 精力 itself.

"He is always full of energy."

他总是充满活力。